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 $247.67   10.584%   $273.8834   $273.88   $273.90   $273.90  
  Purchase #2 $113.62   3.543%   $117.6456   $117.65   $117.65   $117.60  
  Purchase #3 $34.72   10.165%   $38.2493   $38.25   $38.25   $38.20  
  Purchase #4 $241.53   5.447%   $254.6861   $254.69   $254.70   $254.70  
  Purchase #5 $239.62   5.573%   $252.974   $252.97   $252.95   $253.00  
  Purchase #6 $143.27   3.838%   $148.7687   $148.77   $148.75   $148.80  
  Purchase #7 $16.33   11.214%   $18.1612   $18.16   $18.15   $18.20  
  7 purchase totals = $1,036.76       $1,104.3683   $1,104.37   $1,104.35   $1,104.40