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 $128.99   6.850%   $137.8258   $137.83   $137.85   $137.80  
  Purchase #2 $214.75   8.109%   $232.1641   $232.16   $232.15   $232.20  
  Purchase #3 $230.84   11.104%   $256.4725   $256.47   $256.45   $256.50  
  Purchase #4 $116.82   6.201%   $124.064   $124.06   $124.05   $124.10  
  Purchase #5 $8.45   5.735%   $8.9346   $8.93   $8.95   $8.90  
  Purchase #6 $72.76   3.594%   $75.375   $75.38   $75.40   $75.40  
  Purchase #7 $222.91   8.261%   $241.3246   $241.32   $241.30   $241.30  
  7 purchase totals = $995.52       $1,076.1606   $1,076.15   $1,076.15   $1,076.20