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 $162.85   13.339%   $184.5726   $184.57   $184.55   $184.60  
  Purchase #2 $69.86   8.811%   $76.0154   $76.02   $76.00   $76.00  
  Purchase #3 $68.86   4.199%   $71.7514   $71.75   $71.75   $71.80  
  Purchase #4 $79.51   6.745%   $84.8729   $84.87   $84.85   $84.90  
  Purchase #5 $103.39   7.623%   $111.2714   $111.27   $111.25   $111.30  
  Purchase #6 $52.73   8.239%   $57.0744   $57.07   $57.05   $57.10  
  Purchase #7 $82.40   11.196%   $91.6255   $91.63   $91.65   $91.60  
  7 purchase totals = $619.60       $677.1836   $677.18   $677.10   $677.30