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 $68.79   6.466%   $73.238   $73.24   $73.25   $73.20  
  Purchase #2 $46.75   9.751%   $51.3086   $51.31   $51.30   $51.30  
  Purchase #3 $78.76   12.300%   $88.4475   $88.45   $88.45   $88.40  
  Purchase #4 $201.68   10.465%   $222.7858   $222.79   $222.80   $222.80  
  Purchase #5 $141.93   11.152%   $157.758   $157.76   $157.75   $157.80  
  Purchase #6 $18.76   5.456%   $19.7835   $19.78   $19.80   $19.80  
  Purchase #7 $132.89   9.129%   $145.0215   $145.02   $145.00   $145.00  
  7 purchase totals = $689.56       $758.3429   $758.35   $758.35   $758.30