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 $77.96   4.346%   $81.3481   $81.35   $81.35   $81.30  
  Purchase #2 $170.32   7.500%   $183.094   $183.09   $183.10   $183.10  
  Purchase #3 $47.31   8.579%   $51.3687   $51.37   $51.35   $51.40  
  Purchase #4 $87.90   11.282%   $97.8169   $97.82   $97.80   $97.80  
  Purchase #5 $141.36   12.508%   $159.0413   $159.04   $159.05   $159.00  
  Purchase #6 $36.32   9.390%   $39.7304   $39.73   $39.75   $39.70  
  Purchase #7 $205.72   3.187%   $212.2763   $212.28   $212.30   $212.30  
  7 purchase totals = $766.89       $824.6757   $824.68   $824.70   $824.60