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 $120.51   10.379%   $133.0177   $133.02   $133.00   $133.00  
  Purchase #2 $211.82   11.388%   $235.9421   $235.94   $235.95   $235.90  
  Purchase #3 $191.62   12.601%   $215.766   $215.77   $215.75   $215.80  
  Purchase #4 $201.95   10.643%   $223.4435   $223.44   $223.45   $223.40  
  Purchase #5 $245.34   11.209%   $272.8402   $272.84   $272.85   $272.80  
  Purchase #6 $217.67   13.352%   $246.7333   $246.73   $246.75   $246.70  
  Purchase #7 $82.97   11.187%   $92.2519   $92.25   $92.25   $92.30  
  7 purchase totals = $1,271.88       $1,419.9947   $1,419.99   $1,420.00   $1,419.90