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 $5.27   12.670%   $5.9377   $5.94   $5.95   $5.90  
  Purchase #2 $72.69   3.636%   $75.333   $75.33   $75.35   $75.30  
  Purchase #3 $76.38   9.280%   $83.4681   $83.47   $83.45   $83.50  
  Purchase #4 $205.84   7.734%   $221.7597   $221.76   $221.75   $221.80  
  Purchase #5 $131.45   6.658%   $140.2019   $140.20   $140.20   $140.20  
  Purchase #6 $177.84   3.855%   $184.6957   $184.70   $184.70   $184.70  
  Purchase #7 $208.71   3.672%   $216.3738   $216.37   $216.35   $216.40  
  7 purchase totals = $878.18       $927.7699   $927.77   $927.75   $927.80