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 $245.80   8.436%   $266.5357   $266.54   $266.55   $266.50  
  Purchase #2 $175.35   9.546%   $192.0889   $192.09   $192.10   $192.10  
  Purchase #3 $174.27   10.708%   $192.9308   $192.93   $192.95   $192.90  
  Purchase #4 $35.68   6.506%   $38.0013   $38.00   $38.00   $38.00  
  Purchase #5 $98.96   9.531%   $108.3919   $108.39   $108.40   $108.40  
  Purchase #6 $48.53   10.223%   $53.4912   $53.49   $53.50   $53.50  
  Purchase #7 $116.96   7.351%   $125.5577   $125.56   $125.55   $125.60  
  7 purchase totals = $895.55       $976.9975   $977.00   $977.05   $977.00