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 $231.66   5.409%   $244.1905   $244.19   $244.20   $244.20  
  Purchase #2 $70.81   7.160%   $75.88   $75.88   $75.90   $75.90  
  Purchase #3 $172.79   10.257%   $190.5131   $190.51   $190.50   $190.50  
  Purchase #4 $124.40   4.420%   $129.8985   $129.90   $129.90   $129.90  
  Purchase #5 $163.61   8.293%   $177.1782   $177.18   $177.20   $177.20  
  Purchase #6 $67.69   11.539%   $75.5007   $75.50   $75.50   $75.50  
  Purchase #7 $54.65   5.391%   $57.5962   $57.60   $57.60   $57.60  
  7 purchase totals = $885.61       $950.7572   $950.76   $950.80   $950.80