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 $198.61   11.150%   $220.755   $220.76   $220.75   $220.80  
  Purchase #2 $138.54   11.810%   $154.9016   $154.90   $154.90   $154.90  
  Purchase #3 $44.58   3.352%   $46.0743   $46.07   $46.05   $46.10  
  Purchase #4 $121.84   11.667%   $136.0551   $136.06   $136.05   $136.10  
  Purchase #5 $177.36   9.400%   $194.0318   $194.03   $194.05   $194.00  
  Purchase #6 $216.50   9.193%   $236.4028   $236.40   $236.40   $236.40  
  Purchase #7 $34.92   9.529%   $38.2475   $38.25   $38.25   $38.20  
  7 purchase totals = $932.35       $1,026.4681   $1,026.47   $1,026.45   $1,026.50