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 $240.95   8.732%   $261.9898   $261.99   $262.00   $262.00  
  Purchase #2 $202.82   10.742%   $224.6069   $224.61   $224.60   $224.60  
  Purchase #3 $148.66   10.753%   $164.6454   $164.65   $164.65   $164.60  
  Purchase #4 $188.85   7.342%   $202.7154   $202.72   $202.70   $202.70  
  Purchase #5 $87.31   8.548%   $94.7733   $94.77   $94.75   $94.80  
  Purchase #6 $49.25   11.147%   $54.7399   $54.74   $54.75   $54.70  
  Purchase #7 $80.30   4.130%   $83.6164   $83.62   $83.60   $83.60  
  7 purchase totals = $998.14       $1,087.0871   $1,087.10   $1,087.05   $1,087.00