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 $64.43   10.706%   $71.3279   $71.33   $71.35   $71.30  
  Purchase #2 $228.65   8.822%   $248.8215   $248.82   $248.80   $248.80  
  Purchase #3 $201.48   3.516%   $208.564   $208.56   $208.55   $208.60  
  Purchase #4 $230.29   3.468%   $238.2765   $238.28   $238.30   $238.30  
  Purchase #5 $171.54   6.607%   $182.8736   $182.87   $182.85   $182.90  
  Purchase #6 $124.64   13.650%   $141.6534   $141.65   $141.65   $141.70  
  Purchase #7 $238.54   5.586%   $251.8648   $251.86   $251.85   $251.90  
  7 purchase totals = $1,259.57       $1,343.3817   $1,343.37   $1,343.35   $1,343.50