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 $124.28   8.294%   $134.5878   $134.59   $134.60   $134.60  
  Purchase #2 $75.71   9.275%   $82.7321   $82.73   $82.75   $82.70  
  Purchase #3 $10.91   7.131%   $11.688   $11.69   $11.70   $11.70  
  Purchase #4 $150.73   10.353%   $166.3351   $166.34   $166.35   $166.30  
  Purchase #5 $67.57   12.663%   $76.1264   $76.13   $76.15   $76.10  
  Purchase #6 $226.97   6.521%   $241.7707   $241.77   $241.75   $241.80  
  Purchase #7 $54.94   11.651%   $61.3411   $61.34   $61.35   $61.30  
  7 purchase totals = $711.11       $774.5812   $774.59   $774.65   $774.50