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 $210.41   12.379%   $236.4567   $236.46   $236.45   $236.50  
  Purchase #2 $184.49   8.778%   $200.6845   $200.68   $200.70   $200.70  
  Purchase #3 $177.38   13.570%   $201.4505   $201.45   $201.45   $201.50  
  Purchase #4 $184.63   10.494%   $204.0051   $204.01   $204.00   $204.00  
  Purchase #5 $21.93   7.718%   $23.6226   $23.62   $23.60   $23.60  
  Purchase #6 $158.85   11.165%   $176.5856   $176.59   $176.60   $176.60  
  Purchase #7 $68.35   9.424%   $74.7913   $74.79   $74.80   $74.80  
  7 purchase totals = $1,006.04       $1,117.5963   $1,117.60   $1,117.60   $1,117.70