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 $33.53   12.558%   $37.7407   $37.74   $37.75   $37.70  
  Purchase #2 $68.58   11.285%   $76.3193   $76.32   $76.30   $76.30  
  Purchase #3 $227.51   12.165%   $255.1866   $255.19   $255.20   $255.20  
  Purchase #4 $235.61   7.464%   $253.1959   $253.20   $253.20   $253.20  
  Purchase #5 $115.61   7.408%   $124.1744   $124.17   $124.15   $124.20  
  Purchase #6 $202.37   10.829%   $224.2846   $224.28   $224.30   $224.30  
  Purchase #7 $27.30   12.246%   $30.6432   $30.64   $30.65   $30.60  
  7 purchase totals = $910.51       $1,001.5447   $1,001.54   $1,001.55   $1,001.50