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 $248.28   11.246%   $276.2016   $276.20   $276.20   $276.20  
  Purchase #2 $96.62   9.695%   $105.9873   $105.99   $106.00   $106.00  
  Purchase #3 $63.82   7.237%   $68.4387   $68.44   $68.45   $68.40  
  Purchase #4 $219.29   8.538%   $238.013   $238.01   $238.00   $238.00  
  Purchase #5 $210.75   5.613%   $222.5794   $222.58   $222.60   $222.60  
  Purchase #6 $243.50   10.422%   $268.8776   $268.88   $268.90   $268.90  
  Purchase #7 $48.29   11.665%   $53.923   $53.92   $53.90   $53.90  
  7 purchase totals = $1,130.55       $1,234.0206   $1,234.02   $1,234.05   $1,234.00