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 $95.94   7.556%   $103.1892   $103.19   $103.20   $103.20  
  Purchase #2 $54.81   6.146%   $58.1786   $58.18   $58.20   $58.20  
  Purchase #3 $162.65   6.511%   $173.2401   $173.24   $173.25   $173.20  
  Purchase #4 $157.95   5.737%   $167.0116   $167.01   $167.00   $167.00  
  Purchase #5 $96.99   11.491%   $108.1351   $108.14   $108.15   $108.10  
  Purchase #6 $141.69   5.708%   $149.7777   $149.78   $149.80   $149.80  
  Purchase #7 $183.34   3.216%   $189.2362   $189.24   $189.25   $189.20  
  7 purchase totals = $893.37       $948.7685   $948.78   $948.85   $948.70