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 $149.55   12.414%   $168.1151   $168.12   $168.10   $168.10  
  Purchase #2 $231.25   5.783%   $244.6232   $244.62   $244.60   $244.60  
  Purchase #3 $116.51   4.536%   $121.7949   $121.79   $121.80   $121.80  
  Purchase #4 $67.48   8.703%   $73.3528   $73.35   $73.35   $73.40  
  Purchase #5 $63.67   5.769%   $67.3431   $67.34   $67.35   $67.30  
  Purchase #6 $37.28   8.369%   $40.4   $40.40   $40.40   $40.40  
  Purchase #7 $53.26   4.245%   $55.5209   $55.52   $55.50   $55.50  
  7 purchase totals = $719.00       $771.1500   $771.14   $771.10   $771.10