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 $82.84   12.612%   $93.2878   $93.29   $93.30   $93.30  
  Purchase #2 $90.95   4.826%   $95.3392   $95.34   $95.35   $95.30  
  Purchase #3 $105.28   13.658%   $119.6591   $119.66   $119.65   $119.70  
  Purchase #4 $60.77   6.557%   $64.7547   $64.75   $64.75   $64.80  
  Purchase #5 $42.59   13.865%   $48.4951   $48.50   $48.50   $48.50  
  Purchase #6 $177.47   8.581%   $192.6987   $192.70   $192.70   $192.70  
  Purchase #7 $242.95   9.522%   $266.0837   $266.08   $266.10   $266.10  
  7 purchase totals = $802.85       $880.3183   $880.32   $880.35   $880.40