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 $87.78   9.665%   $96.2639   $96.26   $96.25   $96.30  
  Purchase #2 $15.25   11.226%   $16.962   $16.96   $16.95   $17.00  
  Purchase #3 $11.25   11.607%   $12.5558   $12.56   $12.55   $12.60  
  Purchase #4 $217.73   5.871%   $230.5129   $230.51   $230.50   $230.50  
  Purchase #5 $161.41   9.163%   $176.2   $176.20   $176.20   $176.20  
  Purchase #6 $216.77   5.112%   $227.8513   $227.85   $227.85   $227.90  
  Purchase #7 $108.87   3.653%   $112.847   $112.85   $112.85   $112.80  
  7 purchase totals = $819.06       $873.1929   $873.19   $873.15   $873.30