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 $234.61   13.819%   $267.0308   $267.03   $267.05   $267.00  
  Purchase #2 $73.45   13.157%   $83.1138   $83.11   $83.10   $83.10  
  Purchase #3 $162.73   4.567%   $170.1619   $170.16   $170.15   $170.20  
  Purchase #4 $11.26   12.276%   $12.6423   $12.64   $12.65   $12.60  
  Purchase #5 $191.56   8.806%   $208.4288   $208.43   $208.45   $208.40  
  Purchase #6 $204.32   10.317%   $225.3997   $225.40   $225.40   $225.40  
  Purchase #7 $192.95   11.715%   $215.5541   $215.55   $215.55   $215.60  
  7 purchase totals = $1,070.88       $1,182.3314   $1,182.32   $1,182.35   $1,182.30