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 $211.59   11.808%   $236.5745   $236.57   $236.55   $236.60  
  Purchase #2 $182.45   10.867%   $202.2768   $202.28   $202.30   $202.30  
  Purchase #3 $114.65   5.749%   $121.2412   $121.24   $121.25   $121.20  
  Purchase #4 $48.40   13.516%   $54.9417   $54.94   $54.95   $54.90  
  Purchase #5 $127.67   5.640%   $134.8706   $134.87   $134.85   $134.90  
  Purchase #6 $138.87   11.548%   $154.9067   $154.91   $154.90   $154.90  
  Purchase #7 $121.49   3.746%   $126.041   $126.04   $126.05   $126.00  
  7 purchase totals = $945.12       $1,030.8525   $1,030.85   $1,030.85   $1,030.80