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 $126.62   5.807%   $133.9728   $133.97   $133.95   $134.00  
  Purchase #2 $13.44   4.583%   $14.056   $14.06   $14.05   $14.10  
  Purchase #3 $152.67   8.731%   $165.9996   $166.00   $166.00   $166.00  
  Purchase #4 $176.68   8.542%   $191.772   $191.77   $191.75   $191.80  
  Purchase #5 $138.64   11.451%   $154.5157   $154.52   $154.50   $154.50  
  Purchase #6 $241.28   3.758%   $250.3473   $250.35   $250.35   $250.30  
  Purchase #7 $114.39   11.854%   $127.9498   $127.95   $127.95   $127.90  
  7 purchase totals = $963.72       $1,038.6132   $1,038.62   $1,038.55   $1,038.60