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 $178.70   13.764%   $203.2963   $203.30   $203.30   $203.30  
  Purchase #2 $229.72   8.456%   $249.1451   $249.15   $249.15   $249.10  
  Purchase #3 $41.51   13.720%   $47.2052   $47.21   $47.20   $47.20  
  Purchase #4 $40.86   8.228%   $44.222   $44.22   $44.20   $44.20  
  Purchase #5 $81.40   7.567%   $87.5595   $87.56   $87.55   $87.60  
  Purchase #6 $166.87   11.419%   $185.9249   $185.92   $185.90   $185.90  
  Purchase #7 $170.66   13.189%   $193.1683   $193.17   $193.15   $193.20  
  7 purchase totals = $909.72       $1,010.5213   $1,010.53   $1,010.45   $1,010.50