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 $208.93   13.712%   $237.5785   $237.58   $237.60   $237.60  
  Purchase #2 $156.82   12.260%   $176.0461   $176.05   $176.05   $176.00  
  Purchase #3 $175.43   13.582%   $199.2569   $199.26   $199.25   $199.30  
  Purchase #4 $81.73   6.712%   $87.2157   $87.22   $87.20   $87.20  
  Purchase #5 $148.52   13.227%   $168.1647   $168.16   $168.15   $168.20  
  Purchase #6 $100.43   6.664%   $107.1227   $107.12   $107.10   $107.10  
  Purchase #7 $46.30   3.672%   $48.0001   $48.00   $48.00   $48.00  
  7 purchase totals = $918.16       $1,023.3847   $1,023.39   $1,023.35   $1,023.40