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 $102.59   13.390%   $116.3268   $116.33   $116.35   $116.30  
  Purchase #2 $67.76   8.789%   $73.7154   $73.72   $73.70   $73.70  
  Purchase #3 $192.90   5.540%   $203.5867   $203.59   $203.60   $203.60  
  Purchase #4 $201.73   11.193%   $224.3096   $224.31   $224.30   $224.30  
  Purchase #5 $57.30   13.730%   $65.1673   $65.17   $65.15   $65.20  
  Purchase #6 $109.76   4.215%   $114.3864   $114.39   $114.40   $114.40  
  Purchase #7 $221.35   11.776%   $247.4162   $247.42   $247.40   $247.40  
  7 purchase totals = $953.39       $1,044.9084   $1,044.93   $1,044.90   $1,044.90