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 $218.58   3.292%   $225.7757   $225.78   $225.80   $225.80  
  Purchase #2 $213.76   8.488%   $231.9039   $231.90   $231.90   $231.90  
  Purchase #3 $12.70   13.571%   $14.4235   $14.42   $14.40   $14.40  
  Purchase #4 $201.66   10.388%   $222.6084   $222.61   $222.60   $222.60  
  Purchase #5 $53.43   12.582%   $60.1526   $60.15   $60.15   $60.20  
  Purchase #6 $66.45   11.649%   $74.1908   $74.19   $74.20   $74.20  
  Purchase #7 $108.50   11.685%   $121.1782   $121.18   $121.20   $121.20  
  7 purchase totals = $875.08       $950.2331   $950.23   $950.25   $950.30