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 $61.69   11.740%   $68.9324   $68.93   $68.95   $68.90  
  Purchase #2 $157.30   3.532%   $162.8558   $162.86   $162.85   $162.90  
  Purchase #3 $249.67   6.689%   $266.3704   $266.37   $266.35   $266.40  
  Purchase #4 $209.34   11.847%   $234.1405   $234.14   $234.15   $234.10  
  Purchase #5 $196.81   4.509%   $205.6842   $205.68   $205.70   $205.70  
  Purchase #6 $74.40   9.607%   $81.5476   $81.55   $81.55   $81.50  
  Purchase #7 $36.44   4.761%   $38.1749   $38.17   $38.15   $38.20  
  7 purchase totals = $985.65       $1,057.7058   $1,057.70   $1,057.70   $1,057.70