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 $116.41   8.500%   $126.3049   $126.30   $126.30   $126.30  
  Purchase #2 $235.43   5.757%   $248.9837   $248.98   $249.00   $249.00  
  Purchase #3 $236.98   6.441%   $252.2439   $252.24   $252.25   $252.20  
  Purchase #4 $21.89   13.405%   $24.8244   $24.82   $24.80   $24.80  
  Purchase #5 $167.99   12.839%   $189.5582   $189.56   $189.55   $189.60  
  Purchase #6 $231.43   10.261%   $255.177   $255.18   $255.20   $255.20  
  Purchase #7 $87.91   9.787%   $96.5138   $96.51   $96.50   $96.50  
  7 purchase totals = $1,098.04       $1,193.6059   $1,193.59   $1,193.60   $1,193.60