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 $242.41   10.416%   $267.6594   $267.66   $267.65   $267.70  
  Purchase #2 $92.91   13.789%   $105.7214   $105.72   $105.70   $105.70  
  Purchase #3 $213.29   10.254%   $235.1608   $235.16   $235.15   $235.20  
  Purchase #4 $39.62   4.302%   $41.3245   $41.32   $41.30   $41.30  
  Purchase #5 $98.77   7.417%   $106.0958   $106.10   $106.10   $106.10  
  Purchase #6 $22.39   13.716%   $25.461   $25.46   $25.45   $25.50  
  Purchase #7 $33.87   12.295%   $38.0343   $38.03   $38.05   $38.00  
  7 purchase totals = $743.26       $819.4572   $819.45   $819.40   $819.50