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 $120.44   11.722%   $134.558   $134.56   $134.55   $134.60  
  Purchase #2 $173.48   13.421%   $196.7628   $196.76   $196.75   $196.80  
  Purchase #3 $229.39   4.831%   $240.4718   $240.47   $240.45   $240.50  
  Purchase #4 $16.25   9.858%   $17.8519   $17.85   $17.85   $17.90  
  Purchase #5 $106.73   7.432%   $114.6622   $114.66   $114.65   $114.70  
  Purchase #6 $144.50   9.839%   $158.7174   $158.72   $158.70   $158.70  
  Purchase #7 $151.70   7.581%   $163.2004   $163.20   $163.20   $163.20  
  7 purchase totals = $942.49       $1,026.2245   $1,026.22   $1,026.15   $1,026.40