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 $10.53   10.781%   $11.6652   $11.67   $11.65   $11.70  
  Purchase #2 $222.96   10.189%   $245.6774   $245.68   $245.70   $245.70  
  Purchase #3 $159.92   6.223%   $169.8718   $169.87   $169.85   $169.90  
  Purchase #4 $204.58   4.222%   $213.2174   $213.22   $213.20   $213.20  
  Purchase #5 $197.44   11.675%   $220.4911   $220.49   $220.50   $220.50  
  Purchase #6 $66.48   9.731%   $72.9492   $72.95   $72.95   $72.90  
  Purchase #7 $82.90   9.379%   $90.6752   $90.68   $90.70   $90.70  
  7 purchase totals = $944.81       $1,024.5473   $1,024.56   $1,024.55   $1,024.60