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 $48.51   6.425%   $51.6268   $51.63   $51.65   $51.60  
  Purchase #2 $169.61   3.416%   $175.4039   $175.40   $175.40   $175.40  
  Purchase #3 $233.74   7.267%   $250.7259   $250.73   $250.75   $250.70  
  Purchase #4 $197.99   8.772%   $215.3577   $215.36   $215.35   $215.40  
  Purchase #5 $163.33   10.576%   $180.6038   $180.60   $180.60   $180.60  
  Purchase #6 $56.25   11.336%   $62.6265   $62.63   $62.65   $62.60  
  Purchase #7 $71.73   11.298%   $79.8341   $79.83   $79.85   $79.80  
  7 purchase totals = $941.16       $1,016.1787   $1,016.18   $1,016.25   $1,016.10