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 $26.43   10.273%   $29.1452   $29.15   $29.15   $29.10  
  Purchase #2 $73.46   4.332%   $76.6423   $76.64   $76.65   $76.60  
  Purchase #3 $73.63   6.749%   $78.5993   $78.60   $78.60   $78.60  
  Purchase #4 $229.49   7.196%   $246.0041   $246.00   $246.00   $246.00  
  Purchase #5 $62.67   4.521%   $65.5033   $65.50   $65.50   $65.50  
  Purchase #6 $8.52   8.284%   $9.2258   $9.23   $9.25   $9.20  
  Purchase #7 $187.75   8.131%   $203.016   $203.02   $203.00   $203.00  
  7 purchase totals = $661.95       $708.1360   $708.14   $708.15   $708.00