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 $249.81   6.230%   $265.3732   $265.37   $265.35   $265.40  
  Purchase #2 $62.31   10.833%   $69.06   $69.06   $69.05   $69.10  
  Purchase #3 $180.95   7.361%   $194.2697   $194.27   $194.25   $194.30  
  Purchase #4 $191.41   5.542%   $202.0179   $202.02   $202.00   $202.00  
  Purchase #5 $108.39   8.613%   $117.7256   $117.73   $117.75   $117.70  
  Purchase #6 $36.69   12.758%   $41.3709   $41.37   $41.35   $41.40  
  Purchase #7 $149.31   7.653%   $160.7367   $160.74   $160.75   $160.70  
  7 purchase totals = $978.87       $1,050.5540   $1,050.56   $1,050.50   $1,050.60