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 $68.54   3.450%   $70.9046   $70.90   $70.90   $70.90  
  Purchase #2 $14.99   11.331%   $16.6885   $16.69   $16.70   $16.70  
  Purchase #3 $232.32   7.268%   $249.205   $249.21   $249.20   $249.20  
  Purchase #4 $9.41   11.259%   $10.4695   $10.47   $10.45   $10.50  
  Purchase #5 $182.52   10.558%   $201.7905   $201.79   $201.80   $201.80  
  Purchase #6 $160.70   4.603%   $168.097   $168.10   $168.10   $168.10  
  Purchase #7 $217.47   7.848%   $234.537   $234.54   $234.55   $234.50  
  7 purchase totals = $885.95       $951.6921   $951.70   $951.70   $951.70