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 $63.62   13.106%   $71.958   $71.96   $71.95   $72.00  
  Purchase #2 $30.39   6.357%   $32.3219   $32.32   $32.30   $32.30  
  Purchase #3 $138.83   5.597%   $146.6003   $146.60   $146.60   $146.60  
  Purchase #4 $160.70   13.826%   $182.9184   $182.92   $182.90   $182.90  
  Purchase #5 $155.53   7.139%   $166.6333   $166.63   $166.65   $166.60  
  Purchase #6 $156.26   7.633%   $168.1873   $168.19   $168.20   $168.20  
  Purchase #7 $189.62   6.474%   $201.896   $201.90   $201.90   $201.90  
  7 purchase totals = $894.95       $970.5152   $970.52   $970.50   $970.50