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 $243.98   9.546%   $267.2703   $267.27   $267.25   $267.30  
  Purchase #2 $38.63   5.332%   $40.6898   $40.69   $40.70   $40.70  
  Purchase #3 $88.70   4.521%   $92.7101   $92.71   $92.70   $92.70  
  Purchase #4 $244.53   7.426%   $262.6888   $262.69   $262.70   $262.70  
  Purchase #5 $98.37   4.222%   $102.5232   $102.52   $102.50   $102.50  
  Purchase #6 $139.39   9.198%   $152.2111   $152.21   $152.20   $152.20  
  Purchase #7 $215.66   3.668%   $223.5704   $223.57   $223.55   $223.60  
  7 purchase totals = $1,069.26       $1,141.6637   $1,141.66   $1,141.60   $1,141.70