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 $226.99   6.293%   $241.2745   $241.27   $241.25   $241.30  
  Purchase #2 $102.81   13.356%   $116.5413   $116.54   $116.55   $116.50  
  Purchase #3 $104.96   4.408%   $109.5866   $109.59   $109.60   $109.60  
  Purchase #4 $109.98   13.271%   $124.5754   $124.58   $124.60   $124.60  
  Purchase #5 $113.80   5.157%   $119.6687   $119.67   $119.65   $119.70  
  Purchase #6 $206.34   4.304%   $215.2209   $215.22   $215.20   $215.20  
  Purchase #7 $46.69   8.155%   $50.4976   $50.50   $50.50   $50.50  
  7 purchase totals = $911.57       $977.3650   $977.37   $977.35   $977.40