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 $67.84   11.674%   $75.7596   $75.76   $75.75   $75.80  
  Purchase #2 $171.82   13.123%   $194.3679   $194.37   $194.35   $194.40  
  Purchase #3 $13.60   7.577%   $14.6305   $14.63   $14.65   $14.60  
  Purchase #4 $159.88   7.373%   $171.668   $171.67   $171.65   $171.70  
  Purchase #5 $189.62   9.193%   $207.0518   $207.05   $207.05   $207.10  
  Purchase #6 $32.79   11.546%   $36.5759   $36.58   $36.60   $36.60  
  Purchase #7 $171.80   3.226%   $177.3423   $177.34   $177.35   $177.30  
  7 purchase totals = $807.35       $877.3960   $877.40   $877.40   $877.50