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 $54.74   7.213%   $58.6884   $58.69   $58.70   $58.70  
  Purchase #2 $157.49   7.344%   $169.0561   $169.06   $169.05   $169.10  
  Purchase #3 $100.49   3.452%   $103.9589   $103.96   $103.95   $104.00  
  Purchase #4 $39.63   8.572%   $43.0271   $43.03   $43.05   $43.00  
  Purchase #5 $101.32   6.770%   $108.1794   $108.18   $108.20   $108.20  
  Purchase #6 $208.45   9.221%   $227.6712   $227.67   $227.65   $227.70  
  Purchase #7 $193.97   4.293%   $202.2971   $202.30   $202.30   $202.30  
  7 purchase totals = $856.09       $912.8782   $912.89   $912.90   $913.00