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 $68.89   6.257%   $73.2004   $73.20   $73.20   $73.20  
  Purchase #2 $43.54   9.193%   $47.5426   $47.54   $47.55   $47.50  
  Purchase #3 $34.33   5.557%   $36.2377   $36.24   $36.25   $36.20  
  Purchase #4 $84.43   5.169%   $88.7942   $88.79   $88.80   $88.80  
  Purchase #5 $111.31   5.740%   $117.6992   $117.70   $117.70   $117.70  
  Purchase #6 $211.57   11.672%   $236.2645   $236.26   $236.25   $236.30  
  Purchase #7 $158.97   10.286%   $175.3217   $175.32   $175.30   $175.30  
  7 purchase totals = $713.04       $775.0603   $775.05   $775.05   $775.00