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 $58.33   5.296%   $61.4192   $61.42   $61.40   $61.40  
  Purchase #2 $73.86   12.275%   $82.9263   $82.93   $82.95   $82.90  
  Purchase #3 $203.64   10.471%   $224.9631   $224.96   $224.95   $225.00  
  Purchase #4 $137.36   5.787%   $145.309   $145.31   $145.30   $145.30  
  Purchase #5 $35.68   10.314%   $39.36   $39.36   $39.35   $39.40  
  Purchase #6 $155.38   3.369%   $160.6148   $160.61   $160.60   $160.60  
  Purchase #7 $232.63   6.857%   $248.5814   $248.58   $248.60   $248.60  
  7 purchase totals = $896.88       $963.1738   $963.17   $963.15   $963.20