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 $246.87   6.710%   $263.435   $263.44   $263.45   $263.40  
  Purchase #2 $234.49   5.651%   $247.741   $247.74   $247.75   $247.70  
  Purchase #3 $33.99   5.631%   $35.904   $35.90   $35.90   $35.90  
  Purchase #4 $73.73   9.701%   $80.8825   $80.88   $80.90   $80.90  
  Purchase #5 $196.37   12.765%   $221.4366   $221.44   $221.45   $221.40  
  Purchase #6 $226.47   8.234%   $245.1175   $245.12   $245.10   $245.10  
  Purchase #7 $208.35   12.579%   $234.5583   $234.56   $234.55   $234.60  
  7 purchase totals = $1,220.27       $1,329.0749   $1,329.08   $1,329.10   $1,329.00