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 $60.83   7.803%   $65.5766   $65.58   $65.60   $65.60  
  Purchase #2 $123.85   5.394%   $130.5305   $130.53   $130.55   $130.50  
  Purchase #3 $116.50   13.814%   $132.5933   $132.59   $132.60   $132.60  
  Purchase #4 $23.45   9.251%   $25.6194   $25.62   $25.60   $25.60  
  Purchase #5 $120.75   5.402%   $127.2729   $127.27   $127.25   $127.30  
  Purchase #6 $219.77   5.279%   $231.3717   $231.37   $231.35   $231.40  
  Purchase #7 $234.84   13.608%   $266.797   $266.80   $266.80   $266.80  
  7 purchase totals = $899.99       $979.7614   $979.76   $979.75   $979.80