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 $85.51   11.673%   $95.4916   $95.49   $95.50   $95.50  
  Purchase #2 $177.92   12.125%   $199.4928   $199.49   $199.50   $199.50  
  Purchase #3 $224.44   8.257%   $242.972   $242.97   $242.95   $243.00  
  Purchase #4 $60.94   8.250%   $65.9676   $65.97   $65.95   $66.00  
  Purchase #5 $82.81   13.760%   $94.2047   $94.20   $94.20   $94.20  
  Purchase #6 $147.48   12.559%   $166.002   $166.00   $166.00   $166.00  
  Purchase #7 $39.67   7.547%   $42.6639   $42.66   $42.65   $42.70  
  7 purchase totals = $818.77       $906.7946   $906.78   $906.75   $906.90