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 $82.83   5.662%   $87.5198   $87.52   $87.50   $87.50  
  Purchase #2 $148.57   3.457%   $153.7061   $153.71   $153.70   $153.70  
  Purchase #3 $156.41   12.735%   $176.3288   $176.33   $176.35   $176.30  
  Purchase #4 $206.54   13.165%   $233.731   $233.73   $233.75   $233.70  
  Purchase #5 $60.56   8.459%   $65.6828   $65.68   $65.70   $65.70  
  Purchase #6 $137.51   3.238%   $141.9626   $141.96   $141.95   $142.00  
  Purchase #7 $125.73   10.253%   $138.6211   $138.62   $138.60   $138.60  
  7 purchase totals = $918.15       $997.5522   $997.55   $997.55   $997.50