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 $59.47   7.648%   $64.0183   $64.02   $64.00   $64.00  
  Purchase #2 $62.66   9.705%   $68.7412   $68.74   $68.75   $68.70  
  Purchase #3 $149.32   4.864%   $156.5829   $156.58   $156.60   $156.60  
  Purchase #4 $130.85   4.525%   $136.771   $136.77   $136.75   $136.80  
  Purchase #5 $70.32   8.250%   $76.1214   $76.12   $76.10   $76.10  
  Purchase #6 $66.76   4.427%   $69.7155   $69.72   $69.70   $69.70  
  Purchase #7 $190.43   9.219%   $207.9857   $207.99   $208.00   $208.00  
  7 purchase totals = $729.81       $779.9360   $779.94   $779.90   $779.90