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 $207.75   13.581%   $235.9645   $235.96   $235.95   $236.00  
  Purchase #2 $14.74   4.491%   $15.402   $15.40   $15.40   $15.40  
  Purchase #3 $224.74   12.627%   $253.1179   $253.12   $253.10   $253.10  
  Purchase #4 $163.93   3.668%   $169.943   $169.94   $169.95   $169.90  
  Purchase #5 $153.30   7.503%   $164.8021   $164.80   $164.80   $164.80  
  Purchase #6 $27.37   4.687%   $28.6528   $28.65   $28.65   $28.70  
  Purchase #7 $132.79   11.869%   $148.5508   $148.55   $148.55   $148.60  
  7 purchase totals = $924.62       $1,016.4331   $1,016.42   $1,016.40   $1,016.50