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 $174.79   4.277%   $182.2658   $182.27   $182.25   $182.30  
  Purchase #2 $177.26   9.144%   $193.4687   $193.47   $193.45   $193.50  
  Purchase #3 $243.27   11.208%   $270.5357   $270.54   $270.55   $270.50  
  Purchase #4 $214.26   9.527%   $234.6726   $234.67   $234.65   $234.70  
  Purchase #5 $54.90   9.527%   $60.1303   $60.13   $60.15   $60.10  
  Purchase #6 $95.81   9.685%   $105.0892   $105.09   $105.10   $105.10  
  Purchase #7 $106.64   12.777%   $120.2654   $120.27   $120.25   $120.30  
  7 purchase totals = $1,066.93       $1,166.4277   $1,166.44   $1,166.40   $1,166.50