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 $49.94   8.511%   $54.1904   $54.19   $54.20   $54.20  
  Purchase #2 $122.58   7.725%   $132.0493   $132.05   $132.05   $132.00  
  Purchase #3 $58.50   3.460%   $60.5241   $60.52   $60.50   $60.50  
  Purchase #4 $167.78   4.436%   $175.2227   $175.22   $175.20   $175.20  
  Purchase #5 $141.52   10.333%   $156.1433   $156.14   $156.15   $156.10  
  Purchase #6 $36.72   8.268%   $39.756   $39.76   $39.75   $39.80  
  Purchase #7 $54.46   3.176%   $56.1896   $56.19   $56.20   $56.20  
  7 purchase totals = $631.50       $674.0754   $674.07   $674.05   $674.00