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 $128.34   13.439%   $145.5876   $145.59   $145.60   $145.60  
  Purchase #2 $202.35   12.274%   $227.1864   $227.19   $227.20   $227.20  
  Purchase #3 $105.25   11.415%   $117.2643   $117.26   $117.25   $117.30  
  Purchase #4 $229.91   8.730%   $249.9811   $249.98   $250.00   $250.00  
  Purchase #5 $109.96   12.338%   $123.5269   $123.53   $123.55   $123.50  
  Purchase #6 $67.77   11.147%   $75.3243   $75.32   $75.30   $75.30  
  Purchase #7 $13.90   5.338%   $14.642   $14.64   $14.65   $14.60  
  7 purchase totals = $857.48       $953.5126   $953.51   $953.55   $953.50