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 $23.92   4.509%   $24.9986   $25.00   $25.00   $25.00  
  Purchase #2 $118.96   3.282%   $122.8643   $122.86   $122.85   $122.90  
  Purchase #3 $41.50   6.792%   $44.3187   $44.32   $44.30   $44.30  
  Purchase #4 $65.56   3.849%   $68.0834   $68.08   $68.10   $68.10  
  Purchase #5 $248.33   6.284%   $263.9351   $263.94   $263.95   $263.90  
  Purchase #6 $187.38   13.673%   $213.0005   $213.00   $213.00   $213.00  
  Purchase #7 $250.30   10.614%   $276.8668   $276.87   $276.85   $276.90  
  7 purchase totals = $935.95       $1,014.0674   $1,014.07   $1,014.05   $1,014.10