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 $34.32   5.833%   $36.3219   $36.32   $36.30   $36.30  
  Purchase #2 $245.52   11.342%   $273.3669   $273.37   $273.35   $273.40  
  Purchase #3 $166.47   12.181%   $186.7477   $186.75   $186.75   $186.70  
  Purchase #4 $114.49   10.864%   $126.9282   $126.93   $126.95   $126.90  
  Purchase #5 $60.83   7.854%   $65.6076   $65.61   $65.60   $65.60  
  Purchase #6 $110.35   13.550%   $125.3024   $125.30   $125.30   $125.30  
  Purchase #7 $18.56   12.705%   $20.918   $20.92   $20.90   $20.90  
  7 purchase totals = $750.54       $835.1927   $835.20   $835.15   $835.10