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 $184.63   12.135%   $207.0349   $207.03   $207.05   $207.00  
  Purchase #2 $120.30   9.585%   $131.8308   $131.83   $131.85   $131.80  
  Purchase #3 $199.64   8.634%   $216.8769   $216.88   $216.90   $216.90  
  Purchase #4 $57.49   5.418%   $60.6048   $60.60   $60.60   $60.60  
  Purchase #5 $205.69   7.314%   $220.7342   $220.73   $220.75   $220.70  
  Purchase #6 $126.42   7.208%   $135.5324   $135.53   $135.55   $135.50  
  Purchase #7 $65.62   10.181%   $72.3008   $72.30   $72.30   $72.30  
  7 purchase totals = $959.79       $1,044.9148   $1,044.90   $1,045.00   $1,044.80