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	$52.79	8.209%	$57.1235	$57.12	$57.10	$57.10
Purchase #2	$204.48	10.452%	$225.8522	$225.85	$225.85	$225.90
Purchase #3	$105.91	12.494%	$119.1424	$119.14	$119.15	$119.10
Purchase #4	$89.71	4.601%	$93.8376	$93.84	$93.85	$93.80
Purchase #5	$202.79	8.271%	$219.5628	$219.56	$219.55	$219.60
Purchase #6	$103.53	10.531%	$114.4327	$114.43	$114.45	$114.40
Purchase #7	$217.63	6.270%	$231.2754	$231.28	$231.30	$231.30
7 purchase totals =	$976.84		$1,061.2266	$1,061.22	$1,061.25	$1,061.20