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 $113.26   11.726%   $126.5409   $126.54   $126.55   $126.50  
  Purchase #2 $189.86   6.287%   $201.7965   $201.80   $201.80   $201.80  
  Purchase #3 $246.71   3.755%   $255.974   $255.97   $255.95   $256.00  
  Purchase #4 $218.62   8.355%   $236.8857   $236.89   $236.90   $236.90  
  Purchase #5 $49.34   10.198%   $54.3717   $54.37   $54.35   $54.40  
  Purchase #6 $7.29   12.795%   $8.2228   $8.22   $8.20   $8.20  
  Purchase #7 $157.67   5.798%   $166.8117   $166.81   $166.80   $166.80  
  7 purchase totals = $982.75       $1,050.6033   $1,050.60   $1,050.55   $1,050.60