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 $156.26   12.608%   $175.9613   $175.96   $175.95   $176.00  
  Purchase #2 $145.88   12.565%   $164.2098   $164.21   $164.20   $164.20  
  Purchase #3 $58.50   10.432%   $64.6027   $64.60   $64.60   $64.60  
  Purchase #4 $123.51   10.132%   $136.024   $136.02   $136.00   $136.00  
  Purchase #5 $188.58   11.150%   $209.6067   $209.61   $209.60   $209.60  
  Purchase #6 $28.85   7.256%   $30.9434   $30.94   $30.95   $30.90  
  Purchase #7 $69.91   7.168%   $74.9211   $74.92   $74.90   $74.90  
  7 purchase totals = $771.49       $856.2690   $856.26   $856.20   $856.20