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 $231.59   13.450%   $262.7389   $262.74   $262.75   $262.70  
  Purchase #2 $183.76   6.478%   $195.664   $195.66   $195.65   $195.70  
  Purchase #3 $166.48   8.405%   $180.4726   $180.47   $180.45   $180.50  
  Purchase #4 $239.76   5.435%   $252.791   $252.79   $252.80   $252.80  
  Purchase #5 $10.64   8.346%   $11.528   $11.53   $11.55   $11.50  
  Purchase #6 $27.95   4.160%   $29.1127   $29.11   $29.10   $29.10  
  Purchase #7 $246.81   8.571%   $267.9641   $267.96   $267.95   $268.00  
  7 purchase totals = $1,106.99       $1,200.2713   $1,200.26   $1,200.25   $1,200.30