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 $167.98   6.761%   $179.3371   $179.34   $179.35   $179.30  
  Purchase #2 $240.50   9.583%   $263.5471   $263.55   $263.55   $263.50  
  Purchase #3 $56.89   6.409%   $60.5361   $60.54   $60.55   $60.50  
  Purchase #4 $180.32   3.707%   $187.0045   $187.00   $187.00   $187.00  
  Purchase #5 $171.97   12.366%   $193.2358   $193.24   $193.25   $193.20  
  Purchase #6 $57.28   6.277%   $60.8755   $60.88   $60.90   $60.90  
  Purchase #7 $233.46   10.713%   $258.4706   $258.47   $258.45   $258.50  
  7 purchase totals = $1,108.40       $1,203.0067   $1,203.02   $1,203.05   $1,202.90