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 $50.53   12.695%   $56.9448   $56.94   $56.95   $56.90  
  Purchase #2 $142.86   10.293%   $157.5646   $157.56   $157.55   $157.60  
  Purchase #3 $187.53   13.586%   $213.0078   $213.01   $213.00   $213.00  
  Purchase #4 $195.26   5.524%   $206.0462   $206.05   $206.05   $206.00  
  Purchase #5 $117.67   12.626%   $132.527   $132.53   $132.55   $132.50  
  Purchase #6 $121.76   8.671%   $132.3178   $132.32   $132.30   $132.30  
  Purchase #7 $110.83   6.845%   $118.4163   $118.42   $118.40   $118.40  
  7 purchase totals = $926.44       $1,016.8245   $1,016.83   $1,016.80   $1,016.70