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 $51.46   8.554%   $55.8619   $55.86   $55.85   $55.90  
  Purchase #2 $156.88   13.669%   $178.3239   $178.32   $178.30   $178.30  
  Purchase #3 $105.49   12.782%   $118.9737   $118.97   $118.95   $119.00  
  Purchase #4 $225.61   8.702%   $245.2426   $245.24   $245.25   $245.20  
  Purchase #5 $38.97   9.207%   $42.558   $42.56   $42.55   $42.60  
  Purchase #6 $217.71   6.804%   $232.523   $232.52   $232.50   $232.50  
  Purchase #7 $192.62   10.838%   $213.4962   $213.50   $213.50   $213.50  
  7 purchase totals = $988.74       $1,086.9793   $1,086.97   $1,086.90   $1,087.00