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 $55.37   5.863%   $58.6163   $58.62   $58.60   $58.60  
  Purchase #2 $150.66   6.415%   $160.3248   $160.32   $160.30   $160.30  
  Purchase #3 $221.77   3.218%   $228.9066   $228.91   $228.90   $228.90  
  Purchase #4 $22.35   10.866%   $24.7786   $24.78   $24.80   $24.80  
  Purchase #5 $40.46   10.527%   $44.7192   $44.72   $44.70   $44.70  
  Purchase #6 $85.53   5.259%   $90.028   $90.03   $90.05   $90.00  
  Purchase #7 $227.88   11.138%   $253.2613   $253.26   $253.25   $253.30  
  7 purchase totals = $804.02       $860.6348   $860.64   $860.60   $860.60