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 $234.78   12.854%   $264.9586   $264.96   $264.95   $265.00  
  Purchase #2 $214.33   9.633%   $234.9764   $234.98   $235.00   $235.00  
  Purchase #3 $113.64   3.436%   $117.5447   $117.54   $117.55   $117.50  
  Purchase #4 $197.74   12.221%   $221.9058   $221.91   $221.90   $221.90  
  Purchase #5 $192.96   11.216%   $214.6024   $214.60   $214.60   $214.60  
  Purchase #6 $79.99   10.679%   $88.5321   $88.53   $88.55   $88.50  
  Purchase #7 $117.92   3.609%   $122.1757   $122.18   $122.20   $122.20  
  7 purchase totals = $1,151.36       $1,264.6957   $1,264.70   $1,264.75   $1,264.70