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 $90.71   4.752%   $95.0205   $95.02   $95.00   $95.00  
  Purchase #2 $33.99   10.769%   $37.6504   $37.65   $37.65   $37.70  
  Purchase #3 $139.57   6.548%   $148.709   $148.71   $148.70   $148.70  
  Purchase #4 $243.78   13.192%   $275.9395   $275.94   $275.95   $275.90  
  Purchase #5 $230.57   9.676%   $252.88   $252.88   $252.90   $252.90  
  Purchase #6 $121.43   4.544%   $126.9478   $126.95   $126.95   $126.90  
  Purchase #7 $190.40   6.652%   $203.0654   $203.07   $203.05   $203.10  
  7 purchase totals = $1,050.45       $1,140.2126   $1,140.22   $1,140.20   $1,140.20