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 $225.46   10.544%   $249.2325   $249.23   $249.25   $249.20  
  Purchase #2 $162.52   8.141%   $175.7508   $175.75   $175.75   $175.80  
  Purchase #3 $34.49   11.597%   $38.4898   $38.49   $38.50   $38.50  
  Purchase #4 $184.71   11.285%   $205.5545   $205.55   $205.55   $205.60  
  Purchase #5 $217.80   12.708%   $245.478   $245.48   $245.50   $245.50  
  Purchase #6 $5.35   11.384%   $5.959   $5.96   $5.95   $6.00  
  Purchase #7 $38.53   12.624%   $43.394   $43.39   $43.40   $43.40  
  7 purchase totals = $868.86       $963.8586   $963.85   $963.90   $964.00