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 $61.74   6.396%   $65.6889   $65.69   $65.70   $65.70  
  Purchase #2 $182.86   10.705%   $202.4352   $202.44   $202.45   $202.40  
  Purchase #3 $158.46   13.234%   $179.4306   $179.43   $179.45   $179.40  
  Purchase #4 $153.95   4.698%   $161.1826   $161.18   $161.20   $161.20  
  Purchase #5 $245.47   6.623%   $261.7275   $261.73   $261.75   $261.70  
  Purchase #6 $39.89   5.485%   $42.078   $42.08   $42.10   $42.10  
  Purchase #7 $137.26   8.843%   $149.3979   $149.40   $149.40   $149.40  
  7 purchase totals = $979.63       $1,061.9407   $1,061.95   $1,062.05   $1,061.90