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 $244.26   6.748%   $260.7427   $260.74   $260.75   $260.70  
  Purchase #2 $233.57   12.302%   $262.3038   $262.30   $262.30   $262.30  
  Purchase #3 $249.92   6.457%   $266.0573   $266.06   $266.05   $266.10  
  Purchase #4 $137.46   8.861%   $149.6403   $149.64   $149.65   $149.60  
  Purchase #5 $105.50   12.643%   $118.8384   $118.84   $118.85   $118.80  
  Purchase #6 $101.89   8.723%   $110.7779   $110.78   $110.80   $110.80  
  Purchase #7 $239.49   6.653%   $255.4233   $255.42   $255.40   $255.40  
  7 purchase totals = $1,312.09       $1,423.7837   $1,423.78   $1,423.80   $1,423.70