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 $241.33   11.371%   $268.7716   $268.77   $268.75   $268.80  
  Purchase #2 $226.82   5.544%   $239.3949   $239.39   $239.40   $239.40  
  Purchase #3 $56.56   11.254%   $62.9253   $62.93   $62.95   $62.90  
  Purchase #4 $106.98   13.445%   $121.3635   $121.36   $121.35   $121.40  
  Purchase #5 $147.52   9.824%   $162.0124   $162.01   $162.00   $162.00  
  Purchase #6 $202.31   6.720%   $215.9052   $215.91   $215.90   $215.90  
  Purchase #7 $116.68   6.575%   $124.3517   $124.35   $124.35   $124.40  
  7 purchase totals = $1,098.20       $1,194.7246   $1,194.72   $1,194.70   $1,194.80