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 $178.41   3.108%   $183.955   $183.96   $183.95   $184.00  
  Purchase #2 $173.85   13.506%   $197.3302   $197.33   $197.35   $197.30  
  Purchase #3 $62.35   11.735%   $69.6668   $69.67   $69.65   $69.70  
  Purchase #4 $214.28   10.304%   $236.3594   $236.36   $236.35   $236.40  
  Purchase #5 $89.73   5.507%   $94.6714   $94.67   $94.65   $94.70  
  Purchase #6 $23.55   7.296%   $25.2682   $25.27   $25.25   $25.30  
  Purchase #7 $216.45   5.815%   $229.0366   $229.04   $229.05   $229.00  
  7 purchase totals = $958.62       $1,036.2876   $1,036.30   $1,036.25   $1,036.40