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 $82.41   12.313%   $92.5571   $92.56   $92.55   $92.60  
  Purchase #2 $216.38   11.340%   $240.9175   $240.92   $240.90   $240.90  
  Purchase #3 $189.36   6.504%   $201.676   $201.68   $201.70   $201.70  
  Purchase #4 $145.73   5.782%   $154.1561   $154.16   $154.15   $154.20  
  Purchase #5 $202.94   6.410%   $215.9485   $215.95   $215.95   $215.90  
  Purchase #6 $40.36   7.488%   $43.3822   $43.38   $43.40   $43.40  
  Purchase #7 $127.89   8.523%   $138.7901   $138.79   $138.80   $138.80  
  7 purchase totals = $1,005.07       $1,087.4275   $1,087.44   $1,087.45   $1,087.50