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 $83.51   13.839%   $95.0669   $95.07   $95.05   $95.10  
  Purchase #2 $143.64   12.399%   $161.4499   $161.45   $161.45   $161.40  
  Purchase #3 $125.96   13.667%   $143.175   $143.18   $143.20   $143.20  
  Purchase #4 $153.62   4.862%   $161.089   $161.09   $161.10   $161.10  
  Purchase #5 $7.85   5.649%   $8.2934   $8.29   $8.30   $8.30  
  Purchase #6 $226.46   5.767%   $239.5199   $239.52   $239.50   $239.50  
  Purchase #7 $186.50   7.805%   $201.0563   $201.06   $201.05   $201.10  
  7 purchase totals = $927.54       $1,009.6504   $1,009.66   $1,009.65   $1,009.70