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 $124.42   5.432%   $131.1785   $131.18   $131.20   $131.20  
  Purchase #2 $139.87   7.610%   $150.5141   $150.51   $150.50   $150.50  
  Purchase #3 $174.96   10.817%   $193.8854   $193.89   $193.90   $193.90  
  Purchase #4 $121.78   9.207%   $132.9923   $132.99   $133.00   $133.00  
  Purchase #5 $97.80   6.411%   $104.07   $104.07   $104.05   $104.10  
  Purchase #6 $175.42   12.631%   $197.5773   $197.58   $197.60   $197.60  
  Purchase #7 $157.34   8.815%   $171.2095   $171.21   $171.20   $171.20  
  7 purchase totals = $991.59       $1,081.4271   $1,081.43   $1,081.45   $1,081.50