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 $50.44   11.119%   $56.0484   $56.05   $56.05   $56.00  
  Purchase #2 $62.78   4.573%   $65.6509   $65.65   $65.65   $65.70  
  Purchase #3 $171.92   12.787%   $193.9034   $193.90   $193.90   $193.90  
  Purchase #4 $238.35   3.103%   $245.746   $245.75   $245.75   $245.70  
  Purchase #5 $113.82   12.290%   $127.8085   $127.81   $127.80   $127.80  
  Purchase #6 $48.37   4.250%   $50.4257   $50.43   $50.45   $50.40  
  Purchase #7 $201.83   8.381%   $218.7454   $218.75   $218.75   $218.70  
  7 purchase totals = $887.51       $958.3283   $958.34   $958.35   $958.20