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 $42.99   8.812%   $46.7783   $46.78   $46.80   $46.80  
  Purchase #2 $11.53   6.576%   $12.2882   $12.29   $12.30   $12.30  
  Purchase #3 $220.64   11.595%   $246.2232   $246.22   $246.20   $246.20  
  Purchase #4 $224.35   3.360%   $231.8882   $231.89   $231.90   $231.90  
  Purchase #5 $162.50   3.285%   $167.8381   $167.84   $167.85   $167.80  
  Purchase #6 $95.47   8.277%   $103.3721   $103.37   $103.35   $103.40  
  Purchase #7 $203.93   5.725%   $215.605   $215.61   $215.60   $215.60  
  7 purchase totals = $961.41       $1,023.9931   $1,024.00   $1,024.00   $1,024.00