Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.81   11.623%   $244.2423   $244.24   $244.25   $244.20  
  Purchase #2 $231.29   10.421%   $255.3927   $255.39   $255.40   $255.40  
  Purchase #3 $145.60   3.406%   $150.5591   $150.56   $150.55   $150.60  
  Purchase #4 $231.58   13.767%   $263.4616   $263.46   $263.45   $263.50  
  Purchase #5 $228.27   8.801%   $248.36   $248.36   $248.35   $248.40  
  Purchase #6 $184.84   11.532%   $206.1557   $206.16   $206.15   $206.20  
  Purchase #7 $220.88   13.685%   $251.1074   $251.11   $251.10   $251.10  
  7 purchase totals = $1,461.27       $1,619.2788   $1,619.28   $1,619.25   $1,619.40