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 $54.76   12.496%   $61.6028   $61.60   $61.60   $61.60  
  Purchase #2 $50.52   12.321%   $56.7446   $56.74   $56.75   $56.70  
  Purchase #3 $63.49   4.463%   $66.3236   $66.32   $66.30   $66.30  
  Purchase #4 $240.46   9.788%   $263.9962   $264.00   $264.00   $264.00  
  Purchase #5 $60.53   5.813%   $64.0486   $64.05   $64.05   $64.00  
  Purchase #6 $180.99   13.658%   $205.7096   $205.71   $205.70   $205.70  
  Purchase #7 $178.93   8.459%   $194.0657   $194.07   $194.05   $194.10  
  7 purchase totals = $829.68       $912.4911   $912.49   $912.45   $912.40