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 $108.67   6.749%   $116.0041   $116.00   $116.00   $116.00  
  Purchase #2 $236.74   12.443%   $266.1976   $266.20   $266.20   $266.20  
  Purchase #3 $231.47   4.438%   $241.7426   $241.74   $241.75   $241.70  
  Purchase #4 $40.68   12.599%   $45.8053   $45.81   $45.80   $45.80  
  Purchase #5 $249.75   12.822%   $281.7729   $281.77   $281.75   $281.80  
  Purchase #6 $161.64   12.175%   $181.3197   $181.32   $181.30   $181.30  
  Purchase #7 $176.71   3.794%   $183.4144   $183.41   $183.40   $183.40  
  7 purchase totals = $1,205.66       $1,316.2566   $1,316.25   $1,316.20   $1,316.20