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 $114.53   11.385%   $127.5692   $127.57   $127.55   $127.60  
  Purchase #2 $149.73   7.503%   $160.9642   $160.96   $160.95   $161.00  
  Purchase #3 $23.49   5.439%   $24.7676   $24.77   $24.75   $24.80  
  Purchase #4 $96.65   8.112%   $104.4902   $104.49   $104.50   $104.50  
  Purchase #5 $14.53   8.133%   $15.7117   $15.71   $15.70   $15.70  
  Purchase #6 $154.98   8.546%   $168.2246   $168.22   $168.20   $168.20  
  Purchase #7 $57.85   10.732%   $64.0585   $64.06   $64.05   $64.10  
  7 purchase totals = $611.76       $665.7860   $665.78   $665.70   $665.90