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 $60.51   7.188%   $64.8595   $64.86   $64.85   $64.90  
  Purchase #2 $229.95   13.151%   $260.1907   $260.19   $260.20   $260.20  
  Purchase #3 $173.56   8.559%   $188.415   $188.42   $188.40   $188.40  
  Purchase #4 $161.29   8.442%   $174.9061   $174.91   $174.90   $174.90  
  Purchase #5 $64.47   11.559%   $71.9221   $71.92   $71.90   $71.90  
  Purchase #6 $135.53   7.570%   $145.7896   $145.79   $145.80   $145.80  
  Purchase #7 $43.53   3.815%   $45.1907   $45.19   $45.20   $45.20  
  7 purchase totals = $868.84       $951.2737   $951.28   $951.25   $951.30