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 $141.49   12.135%   $158.6598   $158.66   $158.65   $158.70  
  Purchase #2 $53.91   6.861%   $57.6088   $57.61   $57.60   $57.60  
  Purchase #3 $56.26   7.226%   $60.3253   $60.33   $60.35   $60.30  
  Purchase #4 $239.89   3.588%   $248.4973   $248.50   $248.50   $248.50  
  Purchase #5 $197.26   7.275%   $211.6107   $211.61   $211.60   $211.60  
  Purchase #6 $180.55   11.611%   $201.5137   $201.51   $201.50   $201.50  
  Purchase #7 $232.29   11.113%   $258.1044   $258.10   $258.10   $258.10  
  7 purchase totals = $1,101.65       $1,196.3200   $1,196.32   $1,196.30   $1,196.30