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 $23.63   7.829%   $25.48   $25.48   $25.50   $25.50  
  Purchase #2 $41.41   9.304%   $45.2628   $45.26   $45.25   $45.30  
  Purchase #3 $180.51   13.540%   $204.9511   $204.95   $204.95   $205.00  
  Purchase #4 $220.94   3.577%   $228.843   $228.84   $228.85   $228.80  
  Purchase #5 $94.60   7.543%   $101.7357   $101.74   $101.75   $101.70  
  Purchase #6 $186.92   7.293%   $200.5521   $200.55   $200.55   $200.60  
  Purchase #7 $41.84   8.127%   $45.2403   $45.24   $45.25   $45.20  
  7 purchase totals = $789.85       $852.0650   $852.06   $852.10   $852.10