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	$102.52	6.600%	$109.2863	$109.29	$109.30	$109.30
Purchase #2	$161.59	3.791%	$167.7159	$167.72	$167.70	$167.70
Purchase #3	$56.30	9.324%	$61.5494	$61.55	$61.55	$61.50
Purchase #4	$96.73	10.259%	$106.6535	$106.65	$106.65	$106.70
Purchase #5	$87.66	7.423%	$94.167	$94.17	$94.15	$94.20
Purchase #6	$48.31	13.850%	$55.0009	$55.00	$55.00	$55.00
Purchase #7	$187.76	11.380%	$209.1271	$209.13	$209.15	$209.10
7 purchase totals =	$740.87		$803.5001	$803.51	$803.50	$803.50