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 $24.26   8.580%   $26.3415   $26.34   $26.35   $26.30  
  Purchase #2 $36.78   6.523%   $39.1792   $39.18   $39.20   $39.20  
  Purchase #3 $60.80   12.730%   $68.5398   $68.54   $68.55   $68.50  
  Purchase #4 $205.51   3.393%   $212.483   $212.48   $212.50   $212.50  
  Purchase #5 $67.76   7.453%   $72.8102   $72.81   $72.80   $72.80  
  Purchase #6 $234.53   10.285%   $258.6514   $258.65   $258.65   $258.70  
  Purchase #7 $23.76   7.174%   $25.4645   $25.46   $25.45   $25.50  
  7 purchase totals = $653.40       $703.4696   $703.46   $703.50   $703.50