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 $32.32   5.281%   $34.0268   $34.03   $34.05   $34.00  
  Purchase #2 $176.95   8.830%   $192.5747   $192.57   $192.55   $192.60  
  Purchase #3 $45.92   5.872%   $48.6164   $48.62   $48.60   $48.60  
  Purchase #4 $15.28   3.501%   $15.815   $15.82   $15.80   $15.80  
  Purchase #5 $198.72   6.391%   $211.4202   $211.42   $211.40   $211.40  
  Purchase #6 $110.74   8.309%   $119.9414   $119.94   $119.95   $119.90  
  Purchase #7 $167.60   6.357%   $178.2543   $178.25   $178.25   $178.30  
  7 purchase totals = $747.53       $800.6488   $800.65   $800.60   $800.60