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 $203.56   5.428%   $214.6092   $214.61   $214.60   $214.60  
  Purchase #2 $96.69   10.276%   $106.6259   $106.63   $106.65   $106.60  
  Purchase #3 $16.57   3.535%   $17.1557   $17.16   $17.15   $17.20  
  Purchase #4 $7.92   6.873%   $8.4643   $8.46   $8.45   $8.50  
  Purchase #5 $7.33   7.860%   $7.9061   $7.91   $7.90   $7.90  
  Purchase #6 $82.62   11.690%   $92.2783   $92.28   $92.30   $92.30  
  Purchase #7 $119.50   8.408%   $129.5476   $129.55   $129.55   $129.50  
  7 purchase totals = $534.19       $576.5871   $576.60   $576.60   $576.60