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 $59.76   12.519%   $67.2414   $67.24   $67.25   $67.20  
  Purchase #2 $230.60   6.832%   $246.3546   $246.35   $246.35   $246.40  
  Purchase #3 $227.50   12.307%   $255.4984   $255.50   $255.50   $255.50  
  Purchase #4 $66.25   8.686%   $72.0045   $72.00   $72.00   $72.00  
  Purchase #5 $231.32   3.418%   $239.2265   $239.23   $239.25   $239.20  
  Purchase #6 $236.95   6.270%   $251.8068   $251.81   $251.80   $251.80  
  Purchase #7 $85.99   13.160%   $97.3063   $97.31   $97.30   $97.30  
  7 purchase totals = $1,138.37       $1,229.4385   $1,229.44   $1,229.45   $1,229.40