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 $250.62   12.742%   $282.554   $282.55   $282.55   $282.60  
  Purchase #2 $240.27   12.275%   $269.7631   $269.76   $269.75   $269.80  
  Purchase #3 $167.78   5.696%   $177.3367   $177.34   $177.35   $177.30  
  Purchase #4 $44.28   12.229%   $49.695   $49.70   $49.70   $49.70  
  Purchase #5 $227.98   9.642%   $249.9618   $249.96   $249.95   $250.00  
  Purchase #6 $147.92   4.467%   $154.5276   $154.53   $154.55   $154.50  
  Purchase #7 $171.30   7.650%   $184.4045   $184.40   $184.40   $184.40  
  7 purchase totals = $1,250.15       $1,368.2427   $1,368.24   $1,368.25   $1,368.30