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 $71.29   5.565%   $75.2573   $75.26   $75.25   $75.30  
  Purchase #2 $116.77   8.702%   $126.9313   $126.93   $126.95   $126.90  
  Purchase #3 $135.83   11.566%   $151.5401   $151.54   $151.55   $151.50  
  Purchase #4 $51.31   13.722%   $58.3508   $58.35   $58.35   $58.40  
  Purchase #5 $133.88   10.172%   $147.4983   $147.50   $147.50   $147.50  
  Purchase #6 $220.51   7.380%   $236.7836   $236.78   $236.80   $236.80  
  Purchase #7 $101.98   4.372%   $106.4386   $106.44   $106.45   $106.40  
  7 purchase totals = $831.57       $902.8000   $902.80   $902.85   $902.80