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 $177.91   8.752%   $193.4807   $193.48   $193.50   $193.50  
  Purchase #2 $203.98   7.546%   $219.3723   $219.37   $219.35   $219.40  
  Purchase #3 $75.59   8.704%   $82.1694   $82.17   $82.15   $82.20  
  Purchase #4 $218.74   9.488%   $239.4941   $239.49   $239.50   $239.50  
  Purchase #5 $211.82   8.607%   $230.0513   $230.05   $230.05   $230.10  
  Purchase #6 $86.32   9.301%   $94.3486   $94.35   $94.35   $94.30  
  Purchase #7 $218.79   8.784%   $238.0085   $238.01   $238.00   $238.00  
  7 purchase totals = $1,193.15       $1,296.9249   $1,296.92   $1,296.90   $1,297.00