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 $64.73   7.764%   $69.7556   $69.76   $69.75   $69.80  
  Purchase #2 $88.77   3.605%   $91.9702   $91.97   $91.95   $92.00  
  Purchase #3 $125.47   6.424%   $133.5302   $133.53   $133.55   $133.50  
  Purchase #4 $131.45   3.833%   $136.4885   $136.49   $136.50   $136.50  
  Purchase #5 $215.96   13.638%   $245.4126   $245.41   $245.40   $245.40  
  Purchase #6 $100.51   5.175%   $105.7114   $105.71   $105.70   $105.70  
  Purchase #7 $249.78   11.194%   $277.7404   $277.74   $277.75   $277.70  
  7 purchase totals = $976.67       $1,060.6089   $1,060.61   $1,060.60   $1,060.60