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 $54.82   8.505%   $59.4824   $59.48   $59.50   $59.50  
  Purchase #2 $74.39   3.650%   $77.1052   $77.11   $77.10   $77.10  
  Purchase #3 $59.86   5.750%   $63.302   $63.30   $63.30   $63.30  
  Purchase #4 $7.29   8.851%   $7.9352   $7.94   $7.95   $7.90  
  Purchase #5 $112.54   8.367%   $121.9562   $121.96   $121.95   $122.00  
  Purchase #6 $67.96   9.718%   $74.5644   $74.56   $74.55   $74.60  
  Purchase #7 $206.60   9.114%   $225.4295   $225.43   $225.45   $225.40  
  7 purchase totals = $583.46       $629.7749   $629.78   $629.80   $629.80