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 $51.39   10.738%   $56.9083   $56.91   $56.90   $56.90  
  Purchase #2 $194.34   5.361%   $204.7586   $204.76   $204.75   $204.80  
  Purchase #3 $158.36   4.158%   $164.9446   $164.94   $164.95   $164.90  
  Purchase #4 $62.62   7.816%   $67.5144   $67.51   $67.50   $67.50  
  Purchase #5 $125.35   10.474%   $138.4792   $138.48   $138.50   $138.50  
  Purchase #6 $142.72   7.400%   $153.2813   $153.28   $153.30   $153.30  
  Purchase #7 $232.52   3.219%   $240.0048   $240.00   $240.00   $240.00  
  7 purchase totals = $967.30       $1,025.8912   $1,025.88   $1,025.90   $1,025.90