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 $69.86   6.715%   $74.5511   $74.55   $74.55   $74.60  
  Purchase #2 $138.73   4.119%   $144.4443   $144.44   $144.45   $144.40  
  Purchase #3 $194.64   13.549%   $221.0118   $221.01   $221.00   $221.00  
  Purchase #4 $188.37   10.732%   $208.5859   $208.59   $208.60   $208.60  
  Purchase #5 $234.78   12.514%   $264.1604   $264.16   $264.15   $264.20  
  Purchase #6 $94.31   4.862%   $98.8954   $98.90   $98.90   $98.90  
  Purchase #7 $34.33   6.419%   $36.5336   $36.53   $36.55   $36.50  
  7 purchase totals = $955.02       $1,048.1825   $1,048.18   $1,048.20   $1,048.20