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 $107.33   11.732%   $119.922   $119.92   $119.90   $119.90  
  Purchase #2 $233.85   5.434%   $246.5574   $246.56   $246.55   $246.60  
  Purchase #3 $28.73   7.571%   $30.9051   $30.91   $30.90   $30.90  
  Purchase #4 $236.65   3.769%   $245.5693   $245.57   $245.55   $245.60  
  Purchase #5 $134.84   10.158%   $148.537   $148.54   $148.55   $148.50  
  Purchase #6 $146.39   3.494%   $151.5049   $151.50   $151.50   $151.50  
  Purchase #7 $111.29   7.504%   $119.6412   $119.64   $119.65   $119.60  
  7 purchase totals = $999.08       $1,062.6369   $1,062.64   $1,062.60   $1,062.60