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 $133.41   11.510%   $148.7655   $148.77   $148.75   $148.80  
  Purchase #2 $165.82   12.476%   $186.5077   $186.51   $186.50   $186.50  
  Purchase #3 $250.37   6.508%   $266.6641   $266.66   $266.65   $266.70  
  Purchase #4 $106.40   7.406%   $114.28   $114.28   $114.30   $114.30  
  Purchase #5 $80.46   7.581%   $86.5597   $86.56   $86.55   $86.60  
  Purchase #6 $8.86   7.444%   $9.5195   $9.52   $9.50   $9.50  
  Purchase #7 $198.65   7.837%   $214.2182   $214.22   $214.20   $214.20  
  7 purchase totals = $943.97       $1,026.5147   $1,026.52   $1,026.45   $1,026.60