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 $216.40   12.594%   $243.6534   $243.65   $243.65   $243.70  
  Purchase #2 $99.31   3.843%   $103.1265   $103.13   $103.15   $103.10  
  Purchase #3 $195.28   5.746%   $206.5008   $206.50   $206.50   $206.50  
  Purchase #4 $136.60   12.219%   $153.2912   $153.29   $153.30   $153.30  
  Purchase #5 $237.51   12.423%   $267.0159   $267.02   $267.00   $267.00  
  Purchase #6 $191.35   6.382%   $203.562   $203.56   $203.55   $203.60  
  Purchase #7 $45.96   4.681%   $48.1114   $48.11   $48.10   $48.10  
  7 purchase totals = $1,122.41       $1,225.2612   $1,225.26   $1,225.25   $1,225.30