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 $164.62   10.299%   $181.5742   $181.57   $181.55   $181.60  
  Purchase #2 $247.81   5.711%   $261.9624   $261.96   $261.95   $262.00  
  Purchase #3 $148.73   12.465%   $167.2692   $167.27   $167.25   $167.30  
  Purchase #4 $68.64   11.707%   $76.6757   $76.68   $76.70   $76.70  
  Purchase #5 $174.35   13.639%   $198.1296   $198.13   $198.15   $198.10  
  Purchase #6 $139.78   9.355%   $152.8564   $152.86   $152.85   $152.90  
  Purchase #7 $19.77   5.534%   $20.8641   $20.86   $20.85   $20.90  
  7 purchase totals = $963.70       $1,059.3316   $1,059.33   $1,059.30   $1,059.50