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 $53.65   3.409%   $55.4789   $55.48   $55.50   $55.50  
  Purchase #2 $243.80   8.308%   $264.0549   $264.05   $264.05   $264.10  
  Purchase #3 $169.57   7.219%   $181.8113   $181.81   $181.80   $181.80  
  Purchase #4 $161.80   8.594%   $175.7051   $175.71   $175.70   $175.70  
  Purchase #5 $147.95   13.237%   $167.5341   $167.53   $167.55   $167.50  
  Purchase #6 $219.99   3.259%   $227.1595   $227.16   $227.15   $227.20  
  Purchase #7 $24.76   7.706%   $26.668   $26.67   $26.65   $26.70  
  7 purchase totals = $1,021.52       $1,098.4118   $1,098.41   $1,098.40   $1,098.50