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 $209.42   12.760%   $236.142   $236.14   $236.15   $236.10  
  Purchase #2 $166.41   13.486%   $188.8521   $188.85   $188.85   $188.90  
  Purchase #3 $97.58   12.449%   $109.7277   $109.73   $109.75   $109.70  
  Purchase #4 $185.62   5.684%   $196.1706   $196.17   $196.15   $196.20  
  Purchase #5 $57.63   12.718%   $64.9594   $64.96   $64.95   $65.00  
  Purchase #6 $143.68   5.788%   $151.9962   $152.00   $152.00   $152.00  
  Purchase #7 $218.85   11.861%   $244.8078   $244.81   $244.80   $244.80  
  7 purchase totals = $1,079.19       $1,192.6558   $1,192.66   $1,192.65   $1,192.70