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 $237.76   11.202%   $264.3939   $264.39   $264.40   $264.40  
  Purchase #2 $238.95   13.746%   $271.7961   $271.80   $271.80   $271.80  
  Purchase #3 $79.68   6.715%   $85.0305   $85.03   $85.05   $85.00  
  Purchase #4 $250.52   8.536%   $271.9044   $271.90   $271.90   $271.90  
  Purchase #5 $201.63   9.507%   $220.799   $220.80   $220.80   $220.80  
  Purchase #6 $190.97   12.858%   $215.5249   $215.52   $215.50   $215.50  
  Purchase #7 $222.91   5.148%   $234.3854   $234.39   $234.40   $234.40  
  7 purchase totals = $1,422.42       $1,563.8342   $1,563.83   $1,563.85   $1,563.80