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 $159.35   12.681%   $179.5572   $179.56   $179.55   $179.60  
  Purchase #2 $82.39   7.643%   $88.6871   $88.69   $88.70   $88.70  
  Purchase #3 $248.86   4.462%   $259.9641   $259.96   $259.95   $260.00  
  Purchase #4 $23.47   3.728%   $24.345   $24.35   $24.35   $24.30  
  Purchase #5 $245.31   9.505%   $268.6267   $268.63   $268.65   $268.60  
  Purchase #6 $160.79   4.461%   $167.9628   $167.96   $167.95   $168.00  
  Purchase #7 $151.69   6.194%   $161.0857   $161.09   $161.10   $161.10  
  7 purchase totals = $1,071.86       $1,150.2286   $1,150.24   $1,150.25   $1,150.30