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 $186.53   10.438%   $206   $206.00   $206.00   $206.00  
  Purchase #2 $13.62   6.753%   $14.5398   $14.54   $14.55   $14.50  
  Purchase #3 $54.31   10.520%   $60.0234   $60.02   $60.00   $60.00  
  Purchase #4 $229.46   13.703%   $260.9029   $260.90   $260.90   $260.90  
  Purchase #5 $228.45   9.461%   $250.0637   $250.06   $250.05   $250.10  
  Purchase #6 $52.91   3.532%   $54.7788   $54.78   $54.80   $54.80  
  Purchase #7 $146.51   5.276%   $154.2399   $154.24   $154.25   $154.20  
  7 purchase totals = $911.79       $1,000.5485   $1,000.54   $1,000.55   $1,000.50