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 $113.35   4.259%   $118.1776   $118.18   $118.20   $118.20  
  Purchase #2 $163.88   7.532%   $176.2234   $176.22   $176.20   $176.20  
  Purchase #3 $179.55   13.336%   $203.4948   $203.49   $203.50   $203.50  
  Purchase #4 $41.56   10.719%   $46.0148   $46.01   $46.00   $46.00  
  Purchase #5 $173.65   10.679%   $192.1941   $192.19   $192.20   $192.20  
  Purchase #6 $69.74   6.281%   $74.1204   $74.12   $74.10   $74.10  
  Purchase #7 $224.65   12.355%   $252.4055   $252.41   $252.40   $252.40  
  7 purchase totals = $966.38       $1,062.6306   $1,062.62   $1,062.60   $1,062.60