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	$141.88	3.518%	$146.8713	$146.87	$146.85	$146.90
Purchase #2	$187.45	9.747%	$205.7208	$205.72	$205.70	$205.70
Purchase #3	$250.94	12.564%	$282.4681	$282.47	$282.45	$282.50
Purchase #4	$206.36	7.231%	$221.2819	$221.28	$221.30	$221.30
Purchase #5	$61.54	10.137%	$67.7783	$67.78	$67.80	$67.80
Purchase #6	$156.70	9.161%	$171.0553	$171.06	$171.05	$171.10
Purchase #7	$248.51	11.871%	$278.0106	$278.01	$278.00	$278.00
7 purchase totals =	$1,253.38		$1,373.1863	$1,373.19	$1,373.15	$1,373.30