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 $233.91   4.708%   $244.9225   $244.92   $244.90   $244.90  
  Purchase #2 $98.67   4.825%   $103.4308   $103.43   $103.45   $103.40  
  Purchase #3 $94.88   13.821%   $107.9934   $107.99   $108.00   $108.00  
  Purchase #4 $238.26   4.410%   $248.7673   $248.77   $248.75   $248.80  
  Purchase #5 $55.59   12.773%   $62.6905   $62.69   $62.70   $62.70  
  Purchase #6 $23.87   13.817%   $27.1681   $27.17   $27.15   $27.20  
  Purchase #7 $250.60   12.770%   $282.6016   $282.60   $282.60   $282.60  
  7 purchase totals = $995.78       $1,077.5742   $1,077.57   $1,077.55   $1,077.60