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 $61.81   12.622%   $69.6117   $69.61   $69.60   $69.60  
  Purchase #2 $232.41   9.386%   $254.224   $254.22   $254.20   $254.20  
  Purchase #3 $217.89   7.316%   $233.8308   $233.83   $233.85   $233.80  
  Purchase #4 $138.95   5.457%   $146.5325   $146.53   $146.55   $146.50  
  Purchase #5 $188.61   9.230%   $206.0187   $206.02   $206.00   $206.00  
  Purchase #6 $216.54   4.707%   $226.7325   $226.73   $226.75   $226.70  
  Purchase #7 $242.37   13.869%   $275.9843   $275.98   $276.00   $276.00  
  7 purchase totals = $1,298.58       $1,412.9345   $1,412.92   $1,412.95   $1,412.80