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 $234.56   12.413%   $263.6759   $263.68   $263.70   $263.70  
  Purchase #2 $69.73   5.187%   $73.3469   $73.35   $73.35   $73.30  
  Purchase #3 $183.33   4.816%   $192.1592   $192.16   $192.15   $192.20  
  Purchase #4 $151.95   13.465%   $172.4101   $172.41   $172.40   $172.40  
  Purchase #5 $84.38   5.390%   $88.9281   $88.93   $88.95   $88.90  
  Purchase #6 $185.33   4.282%   $193.2658   $193.27   $193.25   $193.30  
  Purchase #7 $249.89   13.642%   $283.98   $283.98   $284.00   $284.00  
  7 purchase totals = $1,159.17       $1,267.7660   $1,267.78   $1,267.80   $1,267.80