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 $118.62   6.248%   $126.0314   $126.03   $126.05   $126.00  
  Purchase #2 $194.86   10.513%   $215.3456   $215.35   $215.35   $215.30  
  Purchase #3 $108.49   11.258%   $120.7038   $120.70   $120.70   $120.70  
  Purchase #4 $230.63   11.686%   $257.5814   $257.58   $257.60   $257.60  
  Purchase #5 $209.96   11.694%   $234.5127   $234.51   $234.50   $234.50  
  Purchase #6 $74.60   8.394%   $80.8619   $80.86   $80.85   $80.90  
  Purchase #7 $203.66   9.327%   $222.6554   $222.66   $222.65   $222.70  
  7 purchase totals = $1,140.82       $1,257.6922   $1,257.69   $1,257.70   $1,257.70