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 $118.78   3.721%   $123.1998   $123.20   $123.20   $123.20  
  Purchase #2 $83.49   10.624%   $92.36   $92.36   $92.35   $92.40  
  Purchase #3 $146.97   4.126%   $153.034   $153.03   $153.05   $153.00  
  Purchase #4 $159.70   5.132%   $167.8958   $167.90   $167.90   $167.90  
  Purchase #5 $230.42   11.424%   $256.7432   $256.74   $256.75   $256.70  
  Purchase #6 $183.38   4.218%   $191.115   $191.12   $191.10   $191.10  
  Purchase #7 $28.67   4.625%   $29.996   $30.00   $30.00   $30.00  
  7 purchase totals = $951.41       $1,014.3438   $1,014.35   $1,014.35   $1,014.30