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 $111.53   8.693%   $121.2253   $121.23   $121.25   $121.20  
  Purchase #2 $181.53   12.161%   $203.6059   $203.61   $203.60   $203.60  
  Purchase #3 $30.73   4.577%   $32.1365   $32.14   $32.15   $32.10  
  Purchase #4 $170.61   10.406%   $188.3637   $188.36   $188.35   $188.40  
  Purchase #5 $62.26   4.822%   $65.2622   $65.26   $65.25   $65.30  
  Purchase #6 $109.74   9.736%   $120.4243   $120.42   $120.40   $120.40  
  Purchase #7 $85.93   9.417%   $94.022   $94.02   $94.00   $94.00  
  7 purchase totals = $752.33       $825.0399   $825.04   $825.00   $825.00