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 $71.91   6.160%   $76.3397   $76.34   $76.35   $76.30  
  Purchase #2 $26.33   3.807%   $27.3324   $27.33   $27.35   $27.30  
  Purchase #3 $239.46   9.249%   $261.6077   $261.61   $261.60   $261.60  
  Purchase #4 $142.86   12.572%   $160.8204   $160.82   $160.80   $160.80  
  Purchase #5 $244.94   6.284%   $260.332   $260.33   $260.35   $260.30  
  Purchase #6 $6.50   6.789%   $6.9413   $6.94   $6.95   $6.90  
  Purchase #7 $237.37   12.824%   $267.8103   $267.81   $267.80   $267.80  
  7 purchase totals = $969.37       $1,061.1838   $1,061.18   $1,061.20   $1,061.00