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 $162.41   12.554%   $182.799   $182.80   $182.80   $182.80  
  Purchase #2 $177.54   8.765%   $193.1014   $193.10   $193.10   $193.10  
  Purchase #3 $230.64   3.143%   $237.889   $237.89   $237.90   $237.90  
  Purchase #4 $79.46   3.869%   $82.5343   $82.53   $82.55   $82.50  
  Purchase #5 $233.58   3.390%   $241.4984   $241.50   $241.50   $241.50  
  Purchase #6 $65.80   11.628%   $73.4512   $73.45   $73.45   $73.50  
  Purchase #7 $234.43   6.442%   $249.532   $249.53   $249.55   $249.50  
  7 purchase totals = $1,183.86       $1,260.8053   $1,260.80   $1,260.85   $1,260.80