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 $249.55   7.532%   $268.3461   $268.35   $268.35   $268.30  
  Purchase #2 $16.26   8.128%   $17.5816   $17.58   $17.60   $17.60  
  Purchase #3 $168.65   6.733%   $180.0052   $180.01   $180.00   $180.00  
  Purchase #4 $13.61   5.449%   $14.3516   $14.35   $14.35   $14.40  
  Purchase #5 $7.47   10.765%   $8.2741   $8.27   $8.25   $8.30  
  Purchase #6 $5.50   12.387%   $6.1813   $6.18   $6.20   $6.20  
  Purchase #7 $242.74   5.293%   $255.5882   $255.59   $255.60   $255.60  
  7 purchase totals = $703.78       $750.3281   $750.33   $750.35   $750.40