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 $195.57   8.522%   $212.2365   $212.24   $212.25   $212.20  
  Purchase #2 $177.49   13.646%   $201.7103   $201.71   $201.70   $201.70  
  Purchase #3 $117.82   13.607%   $133.8518   $133.85   $133.85   $133.90  
  Purchase #4 $23.98   12.762%   $27.0403   $27.04   $27.05   $27.00  
  Purchase #5 $44.53   8.109%   $48.1409   $48.14   $48.15   $48.10  
  Purchase #6 $12.77   6.404%   $13.5878   $13.59   $13.60   $13.60  
  Purchase #7 $82.74   9.315%   $90.4472   $90.45   $90.45   $90.40  
  7 purchase totals = $654.90       $727.0148   $727.02   $727.05   $726.90