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 $58.80   5.529%   $62.0511   $62.05   $62.05   $62.10  
  Purchase #2 $164.81   5.218%   $173.4098   $173.41   $173.40   $173.40  
  Purchase #3 $204.77   13.407%   $232.2235   $232.22   $232.20   $232.20  
  Purchase #4 $197.26   7.446%   $211.948   $211.95   $211.95   $211.90  
  Purchase #5 $120.94   11.276%   $134.5772   $134.58   $134.60   $134.60  
  Purchase #6 $65.39   6.658%   $69.7437   $69.74   $69.75   $69.70  
  Purchase #7 $21.33   6.611%   $22.7401   $22.74   $22.75   $22.70  
  7 purchase totals = $833.30       $906.6934   $906.69   $906.70   $906.60