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 $209.53   6.696%   $223.5601   $223.56   $223.55   $223.60  
  Purchase #2 $5.57   8.186%   $6.026   $6.03   $6.05   $6.00  
  Purchase #3 $25.87   12.266%   $29.0432   $29.04   $29.05   $29.00  
  Purchase #4 $89.42   8.375%   $96.9089   $96.91   $96.90   $96.90  
  Purchase #5 $214.40   9.228%   $234.1848   $234.18   $234.20   $234.20  
  Purchase #6 $170.81   6.557%   $182.01   $182.01   $182.00   $182.00  
  Purchase #7 $213.66   12.466%   $240.2949   $240.29   $240.30   $240.30  
  7 purchase totals = $929.26       $1,012.0279   $1,012.02   $1,012.05   $1,012.00