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 $202.92   6.579%   $216.2701   $216.27   $216.25   $216.30  
  Purchase #2 $113.47   12.410%   $127.5516   $127.55   $127.55   $127.60  
  Purchase #3 $244.30   8.214%   $264.3668   $264.37   $264.35   $264.40  
  Purchase #4 $205.54   7.441%   $220.8342   $220.83   $220.85   $220.80  
  Purchase #5 $149.60   3.696%   $155.1292   $155.13   $155.15   $155.10  
  Purchase #6 $201.32   3.543%   $208.4528   $208.45   $208.45   $208.50  
  Purchase #7 $9.88   10.656%   $10.9328   $10.93   $10.95   $10.90  
  7 purchase totals = $1,127.03       $1,203.5375   $1,203.53   $1,203.55   $1,203.60