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 $31.43   5.332%   $33.1058   $33.11   $33.10   $33.10  
  Purchase #2 $173.99   6.148%   $184.6869   $184.69   $184.70   $184.70  
  Purchase #3 $92.61   5.344%   $97.5591   $97.56   $97.55   $97.60  
  Purchase #4 $77.57   10.214%   $85.493   $85.49   $85.50   $85.50  
  Purchase #5 $97.30   12.867%   $109.8196   $109.82   $109.80   $109.80  
  Purchase #6 $135.68   5.477%   $143.1112   $143.11   $143.10   $143.10  
  Purchase #7 $151.40   12.526%   $170.3644   $170.36   $170.35   $170.40  
  7 purchase totals = $759.98       $824.1400   $824.14   $824.10   $824.20