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 $211.89   13.766%   $241.0588   $241.06   $241.05   $241.10  
  Purchase #2 $220.32   4.515%   $230.2674   $230.27   $230.25   $230.30  
  Purchase #3 $88.58   8.694%   $96.2811   $96.28   $96.30   $96.30  
  Purchase #4 $186.96   7.785%   $201.5148   $201.51   $201.50   $201.50  
  Purchase #5 $237.81   7.416%   $255.446   $255.45   $255.45   $255.40  
  Purchase #6 $123.50   3.220%   $127.4767   $127.48   $127.50   $127.50  
  Purchase #7 $14.43   3.784%   $14.976   $14.98   $15.00   $15.00  
  7 purchase totals = $1,083.49       $1,167.0208   $1,167.03   $1,167.05   $1,167.10