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 $240.70   11.791%   $269.0809   $269.08   $269.10   $269.10  
  Purchase #2 $155.66   11.710%   $173.8878   $173.89   $173.90   $173.90  
  Purchase #3 $164.92   6.819%   $176.1659   $176.17   $176.15   $176.20  
  Purchase #4 $189.86   9.175%   $207.2797   $207.28   $207.30   $207.30  
  Purchase #5 $16.46   10.559%   $18.198   $18.20   $18.20   $18.20  
  Purchase #6 $138.93   9.623%   $152.2992   $152.30   $152.30   $152.30  
  Purchase #7 $236.71   11.303%   $263.4653   $263.47   $263.45   $263.50  
  7 purchase totals = $1,143.24       $1,260.3768   $1,260.39   $1,260.40   $1,260.50