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 $207.83   13.813%   $236.5376   $236.54   $236.55   $236.50  
  Purchase #2 $114.71   5.243%   $120.7242   $120.72   $120.70   $120.70  
  Purchase #3 $222.43   10.477%   $245.734   $245.73   $245.75   $245.70  
  Purchase #4 $45.55   6.107%   $48.3317   $48.33   $48.35   $48.30  
  Purchase #5 $87.45   6.715%   $93.3223   $93.32   $93.30   $93.30  
  Purchase #6 $20.67   8.157%   $22.3561   $22.36   $22.35   $22.40  
  Purchase #7 $223.63   10.439%   $246.9747   $246.97   $246.95   $247.00  
  7 purchase totals = $922.27       $1,013.9806   $1,013.97   $1,013.95   $1,013.90