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 $217.78   8.185%   $235.6053   $235.61   $235.60   $235.60  
  Purchase #2 $222.30   12.325%   $249.6985   $249.70   $249.70   $249.70  
  Purchase #3 $105.63   4.869%   $110.7731   $110.77   $110.75   $110.80  
  Purchase #4 $226.74   11.745%   $253.3706   $253.37   $253.35   $253.40  
  Purchase #5 $44.98   8.715%   $48.9   $48.90   $48.90   $48.90  
  Purchase #6 $35.89   9.419%   $39.2705   $39.27   $39.25   $39.30  
  Purchase #7 $131.40   5.678%   $138.8609   $138.86   $138.85   $138.90  
  7 purchase totals = $984.72       $1,076.4789   $1,076.48   $1,076.40   $1,076.60