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	$17.31	7.212%	$18.5584	$18.56	$18.55	$18.60
Purchase #2	$245.78	7.655%	$264.5945	$264.59	$264.60	$264.60
Purchase #3	$187.79	11.338%	$209.0816	$209.08	$209.10	$209.10
Purchase #4	$201.37	7.610%	$216.6943	$216.69	$216.70	$216.70
Purchase #5	$101.39	13.126%	$114.6985	$114.70	$114.70	$114.70
Purchase #6	$41.54	9.757%	$45.5931	$45.59	$45.60	$45.60
Purchase #7	$51.69	7.506%	$55.5699	$55.57	$55.55	$55.60
7 purchase totals =	$846.87		$924.7903	$924.78	$924.80	$924.90