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 $54.63   3.611%   $56.6027   $56.60   $56.60   $56.60  
  Purchase #2 $149.33   11.572%   $166.6105   $166.61   $166.60   $166.60  
  Purchase #3 $146.35   11.552%   $163.2564   $163.26   $163.25   $163.30  
  Purchase #4 $177.25   4.534%   $185.2865   $185.29   $185.30   $185.30  
  Purchase #5 $98.40   12.348%   $110.5504   $110.55   $110.55   $110.60  
  Purchase #6 $15.91   9.224%   $17.3775   $17.38   $17.40   $17.40  
  Purchase #7 $229.31   7.714%   $246.999   $247.00   $247.00   $247.00  
  7 purchase totals = $871.18       $946.6830   $946.69   $946.70   $946.80