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 $49.77   4.849%   $52.1833   $52.18   $52.20   $52.20  
  Purchase #2 $131.96   11.814%   $147.5498   $147.55   $147.55   $147.50  
  Purchase #3 $164.38   13.631%   $186.7866   $186.79   $186.80   $186.80  
  Purchase #4 $80.95   7.218%   $86.793   $86.79   $86.80   $86.80  
  Purchase #5 $197.82   12.174%   $221.9026   $221.90   $221.90   $221.90  
  Purchase #6 $134.49   6.426%   $143.1323   $143.13   $143.15   $143.10  
  Purchase #7 $124.93   8.130%   $135.0868   $135.09   $135.10   $135.10  
  7 purchase totals = $884.30       $973.4344   $973.43   $973.50   $973.40