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 $232.53   10.534%   $257.0247   $257.02   $257.00   $257.00  
  Purchase #2 $193.84   11.453%   $216.0405   $216.04   $216.05   $216.00  
  Purchase #3 $105.43   6.523%   $112.3072   $112.31   $112.30   $112.30  
  Purchase #4 $29.67   3.740%   $30.7797   $30.78   $30.80   $30.80  
  Purchase #5 $177.64   8.685%   $193.068   $193.07   $193.05   $193.10  
  Purchase #6 $239.68   5.399%   $252.6203   $252.62   $252.60   $252.60  
  Purchase #7 $11.31   4.354%   $11.8024   $11.80   $11.80   $11.80  
  7 purchase totals = $990.10       $1,073.6428   $1,073.64   $1,073.60   $1,073.60