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 $236.49   11.791%   $264.3745   $264.37   $264.35   $264.40  
  Purchase #2 $207.79   3.743%   $215.5676   $215.57   $215.55   $215.60  
  Purchase #3 $226.45   8.170%   $244.951   $244.95   $244.95   $245.00  
  Purchase #4 $205.71   7.727%   $221.6052   $221.61   $221.60   $221.60  
  Purchase #5 $158.51   6.715%   $169.1539   $169.15   $169.15   $169.20  
  Purchase #6 $245.47   9.389%   $268.5172   $268.52   $268.50   $268.50  
  Purchase #7 $64.76   4.389%   $67.6023   $67.60   $67.60   $67.60  
  7 purchase totals = $1,345.18       $1,451.7717   $1,451.77   $1,451.70   $1,451.90