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 $243.27   8.515%   $263.9844   $263.98   $264.00   $264.00  
  Purchase #2 $46.41   7.238%   $49.7692   $49.77   $49.75   $49.80  
  Purchase #3 $91.66   4.342%   $95.6399   $95.64   $95.65   $95.60  
  Purchase #4 $186.69   7.853%   $201.3508   $201.35   $201.35   $201.40  
  Purchase #5 $140.44   8.652%   $152.5909   $152.59   $152.60   $152.60  
  Purchase #6 $194.68   6.263%   $206.8728   $206.87   $206.85   $206.90  
  Purchase #7 $175.51   10.292%   $193.5735   $193.57   $193.55   $193.60  
  7 purchase totals = $1,078.66       $1,163.7815   $1,163.77   $1,163.75   $1,163.90