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 $93.69   12.665%   $105.5558   $105.56   $105.55   $105.60  
  Purchase #2 $176.80   10.499%   $195.3622   $195.36   $195.35   $195.40  
  Purchase #3 $76.30   7.719%   $82.1896   $82.19   $82.20   $82.20  
  Purchase #4 $224.98   5.149%   $236.5642   $236.56   $236.55   $236.60  
  Purchase #5 $247.57   6.736%   $264.2463   $264.25   $264.25   $264.20  
  Purchase #6 $128.70   5.439%   $135.7   $135.70   $135.70   $135.70  
  Purchase #7 $233.74   11.623%   $260.9076   $260.91   $260.90   $260.90  
  7 purchase totals = $1,181.78       $1,280.5257   $1,280.53   $1,280.50   $1,280.60