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 $36.81   5.758%   $38.9295   $38.93   $38.95   $38.90  
  Purchase #2 $164.32   7.722%   $177.0088   $177.01   $177.00   $177.00  
  Purchase #3 $167.98   8.450%   $182.1743   $182.17   $182.15   $182.20  
  Purchase #4 $66.58   7.367%   $71.4849   $71.48   $71.50   $71.50  
  Purchase #5 $34.28   8.490%   $37.1904   $37.19   $37.20   $37.20  
  Purchase #6 $218.39   5.322%   $230.0127   $230.01   $230.00   $230.00  
  Purchase #7 $24.43   8.345%   $26.4687   $26.47   $26.45   $26.50  
  7 purchase totals = $712.79       $763.2693   $763.26   $763.25   $763.30