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 $163.94   6.487%   $174.5748   $174.57   $174.55   $174.60  
  Purchase #2 $85.83   11.811%   $95.9674   $95.97   $95.95   $96.00  
  Purchase #3 $217.68   13.802%   $247.7242   $247.72   $247.70   $247.70  
  Purchase #4 $15.62   8.521%   $16.951   $16.95   $16.95   $17.00  
  Purchase #5 $110.83   13.550%   $125.8475   $125.85   $125.85   $125.80  
  Purchase #6 $61.26   5.501%   $64.6299   $64.63   $64.65   $64.60  
  Purchase #7 $152.79   6.493%   $162.7107   $162.71   $162.70   $162.70  
  7 purchase totals = $807.95       $888.4055   $888.40   $888.35   $888.40