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 $57.32   10.329%   $63.2406   $63.24   $63.25   $63.20  
  Purchase #2 $195.34   4.859%   $204.8316   $204.83   $204.85   $204.80  
  Purchase #3 $60.69   12.435%   $68.2368   $68.24   $68.25   $68.20  
  Purchase #4 $35.35   12.624%   $39.8126   $39.81   $39.80   $39.80  
  Purchase #5 $25.46   4.296%   $26.5538   $26.55   $26.55   $26.60  
  Purchase #6 $207.66   6.818%   $221.8183   $221.82   $221.80   $221.80  
  Purchase #7 $187.60   9.184%   $204.8292   $204.83   $204.85   $204.80  
  7 purchase totals = $769.42       $829.3229   $829.32   $829.35   $829.20