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 $89.26   13.532%   $101.3387   $101.34   $101.35   $101.30  
  Purchase #2 $159.77   10.122%   $175.9419   $175.94   $175.95   $175.90  
  Purchase #3 $92.95   13.690%   $105.6749   $105.67   $105.65   $105.70  
  Purchase #4 $231.88   5.685%   $245.0624   $245.06   $245.05   $245.10  
  Purchase #5 $67.71   11.530%   $75.517   $75.52   $75.50   $75.50  
  Purchase #6 $134.96   5.241%   $142.0333   $142.03   $142.05   $142.00  
  Purchase #7 $35.68   10.196%   $39.3179   $39.32   $39.30   $39.30  
  7 purchase totals = $812.21       $884.8861   $884.88   $884.85   $884.80