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 $57.89   7.275%   $62.1015   $62.10   $62.10   $62.10  
  Purchase #2 $158.64   11.116%   $176.2744   $176.27   $176.25   $176.30  
  Purchase #3 $122.60   9.613%   $134.3855   $134.39   $134.40   $134.40  
  Purchase #4 $182.70   6.301%   $194.2119   $194.21   $194.20   $194.20  
  Purchase #5 $190.57   8.777%   $207.2963   $207.30   $207.30   $207.30  
  Purchase #6 $198.29   13.393%   $224.847   $224.85   $224.85   $224.80  
  Purchase #7 $43.51   7.425%   $46.7406   $46.74   $46.75   $46.70  
  7 purchase totals = $954.20       $1,045.8572   $1,045.86   $1,045.85   $1,045.80