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 $49.83   13.247%   $56.431   $56.43   $56.45   $56.40  
  Purchase #2 $151.45   10.302%   $167.0524   $167.05   $167.05   $167.10  
  Purchase #3 $158.63   9.833%   $174.2281   $174.23   $174.25   $174.20  
  Purchase #4 $170.50   7.348%   $183.0283   $183.03   $183.05   $183.00  
  Purchase #5 $188.93   9.845%   $207.5302   $207.53   $207.55   $207.50  
  Purchase #6 $66.60   12.288%   $74.7838   $74.78   $74.80   $74.80  
  Purchase #7 $207.83   8.338%   $225.1589   $225.16   $225.15   $225.20  
  7 purchase totals = $993.77       $1,088.2127   $1,088.21   $1,088.30   $1,088.20