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 $123.94   7.869%   $133.6928   $133.69   $133.70   $133.70  
  Purchase #2 $13.41   13.633%   $15.2382   $15.24   $15.25   $15.20  
  Purchase #3 $176.94   9.634%   $193.9864   $193.99   $194.00   $194.00  
  Purchase #4 $60.48   6.320%   $64.3023   $64.30   $64.30   $64.30  
  Purchase #5 $222.84   8.424%   $241.612   $241.61   $241.60   $241.60  
  Purchase #6 $133.45   6.594%   $142.2497   $142.25   $142.25   $142.20  
  Purchase #7 $229.32   11.258%   $255.1368   $255.14   $255.15   $255.10  
  7 purchase totals = $960.38       $1,046.2182   $1,046.22   $1,046.25   $1,046.10