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 $24.74   6.307%   $26.3004   $26.30   $26.30   $26.30  
  Purchase #2 $192.88   12.661%   $217.3005   $217.30   $217.30   $217.30  
  Purchase #3 $48.92   9.149%   $53.3957   $53.40   $53.40   $53.40  
  Purchase #4 $84.28   3.654%   $87.3596   $87.36   $87.35   $87.40  
  Purchase #5 $168.62   13.406%   $191.2252   $191.23   $191.25   $191.20  
  Purchase #6 $172.94   13.219%   $195.8009   $195.80   $195.80   $195.80  
  Purchase #7 $231.66   6.439%   $246.5766   $246.58   $246.60   $246.60  
  7 purchase totals = $924.04       $1,017.9589   $1,017.97   $1,018.00   $1,018.00