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 $107.43   13.726%   $122.1758   $122.18   $122.20   $122.20  
  Purchase #2 $50.25   12.559%   $56.5609   $56.56   $56.55   $56.60  
  Purchase #3 $156.70   9.755%   $171.9861   $171.99   $172.00   $172.00  
  Purchase #4 $241.66   10.502%   $267.0391   $267.04   $267.05   $267.00  
  Purchase #5 $232.65   5.777%   $246.0902   $246.09   $246.10   $246.10  
  Purchase #6 $52.44   5.794%   $55.4784   $55.48   $55.50   $55.50  
  Purchase #7 $197.99   4.197%   $206.2996   $206.30   $206.30   $206.30  
  7 purchase totals = $1,039.12       $1,125.6301   $1,125.64   $1,125.70   $1,125.70