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 $201.35   11.576%   $224.6583   $224.66   $224.65   $224.70  
  Purchase #2 $29.46   4.256%   $30.7138   $30.71   $30.70   $30.70  
  Purchase #3 $117.66   10.800%   $130.3673   $130.37   $130.35   $130.40  
  Purchase #4 $67.36   13.573%   $76.5028   $76.50   $76.50   $76.50  
  Purchase #5 $203.73   4.225%   $212.3376   $212.34   $212.35   $212.30  
  Purchase #6 $241.35   4.464%   $252.1239   $252.12   $252.10   $252.10  
  Purchase #7 $104.41   12.397%   $117.3537   $117.35   $117.35   $117.40  
  7 purchase totals = $965.32       $1,044.0574   $1,044.05   $1,044.00   $1,044.10