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 $85.77   9.303%   $93.7492   $93.75   $93.75   $93.70  
  Purchase #2 $135.30   10.856%   $149.9882   $149.99   $150.00   $150.00  
  Purchase #3 $7.73   4.398%   $8.07   $8.07   $8.05   $8.10  
  Purchase #4 $24.47   12.811%   $27.6049   $27.60   $27.60   $27.60  
  Purchase #5 $211.40   4.825%   $221.6001   $221.60   $221.60   $221.60  
  Purchase #6 $133.25   10.851%   $147.709   $147.71   $147.70   $147.70  
  Purchase #7 $250.75   9.626%   $274.8872   $274.89   $274.90   $274.90  
  7 purchase totals = $848.67       $923.6086   $923.61   $923.60   $923.60