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 $24.65   6.229%   $26.1854   $26.19   $26.20   $26.20  
  Purchase #2 $181.60   4.654%   $190.0517   $190.05   $190.05   $190.10  
  Purchase #3 $215.37   9.578%   $235.9981   $236.00   $236.00   $236.00  
  Purchase #4 $206.81   10.783%   $229.1103   $229.11   $229.10   $229.10  
  Purchase #5 $73.43   6.181%   $77.9687   $77.97   $77.95   $78.00  
  Purchase #6 $173.65   13.749%   $197.5251   $197.53   $197.55   $197.50  
  Purchase #7 $53.27   13.265%   $60.3363   $60.34   $60.35   $60.30  
  7 purchase totals = $928.78       $1,017.1756   $1,017.19   $1,017.20   $1,017.20