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 $248.67   7.286%   $266.7881   $266.79   $266.80   $266.80  
  Purchase #2 $58.87   11.110%   $65.4105   $65.41   $65.40   $65.40  
  Purchase #3 $246.60   10.677%   $272.9295   $272.93   $272.95   $272.90  
  Purchase #4 $158.94   3.736%   $164.878   $164.88   $164.90   $164.90  
  Purchase #5 $44.56   4.661%   $46.6369   $46.64   $46.65   $46.60  
  Purchase #6 $212.41   8.311%   $230.0634   $230.06   $230.05   $230.10  
  Purchase #7 $91.27   5.104%   $95.9284   $95.93   $95.95   $95.90  
  7 purchase totals = $1,061.32       $1,142.6348   $1,142.64   $1,142.70   $1,142.60