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 $52.74   12.382%   $59.2703   $59.27   $59.25   $59.30  
  Purchase #2 $149.42   3.183%   $154.176   $154.18   $154.20   $154.20  
  Purchase #3 $153.83   6.430%   $163.7213   $163.72   $163.70   $163.70  
  Purchase #4 $54.29   8.222%   $58.7537   $58.75   $58.75   $58.80  
  Purchase #5 $102.64   13.294%   $116.285   $116.29   $116.30   $116.30  
  Purchase #6 $227.32   4.557%   $237.679   $237.68   $237.70   $237.70  
  Purchase #7 $53.62   3.595%   $55.5476   $55.55   $55.55   $55.50  
  7 purchase totals = $793.86       $845.4329   $845.44   $845.45   $845.50