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 $206.66   9.337%   $225.9558   $225.96   $225.95   $226.00  
  Purchase #2 $80.81   13.229%   $91.5004   $91.50   $91.50   $91.50  
  Purchase #3 $200.91   11.702%   $224.4205   $224.42   $224.40   $224.40  
  Purchase #4 $106.46   12.477%   $119.743   $119.74   $119.75   $119.70  
  Purchase #5 $145.41   5.663%   $153.6446   $153.64   $153.65   $153.60  
  Purchase #6 $185.99   6.513%   $198.1035   $198.10   $198.10   $198.10  
  Purchase #7 $23.27   5.553%   $24.5622   $24.56   $24.55   $24.60  
  7 purchase totals = $949.51       $1,037.9300   $1,037.92   $1,037.90   $1,037.90