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 $205.94   9.115%   $224.7114   $224.71   $224.70   $224.70  
  Purchase #2 $248.51   11.721%   $277.6379   $277.64   $277.65   $277.60  
  Purchase #3 $245.31   13.254%   $277.8234   $277.82   $277.80   $277.80  
  Purchase #4 $69.92   9.754%   $76.74   $76.74   $76.75   $76.70  
  Purchase #5 $78.48   4.316%   $81.8672   $81.87   $81.85   $81.90  
  Purchase #6 $24.71   8.178%   $26.7308   $26.73   $26.75   $26.70  
  Purchase #7 $244.87   9.292%   $267.6233   $267.62   $267.60   $267.60  
  7 purchase totals = $1,117.74       $1,233.1340   $1,233.13   $1,233.10   $1,233.00