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 $59.51   7.318%   $63.8649   $63.86   $63.85   $63.90  
  Purchase #2 $145.92   4.751%   $152.8527   $152.85   $152.85   $152.90  
  Purchase #3 $207.78   12.477%   $233.7047   $233.70   $233.70   $233.70  
  Purchase #4 $41.76   3.346%   $43.1573   $43.16   $43.15   $43.20  
  Purchase #5 $225.89   8.259%   $244.5463   $244.55   $244.55   $244.50  
  Purchase #6 $113.57   6.770%   $121.2587   $121.26   $121.25   $121.30  
  Purchase #7 $74.74   13.575%   $84.886   $84.89   $84.90   $84.90  
  7 purchase totals = $869.17       $944.2706   $944.27   $944.25   $944.40