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 $41.42   5.837%   $43.8377   $43.84   $43.85   $43.80  
  Purchase #2 $162.32   13.398%   $184.0676   $184.07   $184.05   $184.10  
  Purchase #3 $212.47   4.403%   $221.8251   $221.83   $221.85   $221.80  
  Purchase #4 $108.77   11.503%   $121.2818   $121.28   $121.30   $121.30  
  Purchase #5 $118.78   8.559%   $128.9464   $128.95   $128.95   $128.90  
  Purchase #6 $234.88   7.779%   $253.1513   $253.15   $253.15   $253.20  
  Purchase #7 $54.36   11.469%   $60.5945   $60.59   $60.60   $60.60  
  7 purchase totals = $933.00       $1,013.7044   $1,013.71   $1,013.75   $1,013.70