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	$159.82	13.160%	$180.8523	$180.85	$180.85	$180.90
Purchase #2	$40.92	11.600%	$45.6667	$45.67	$45.65	$45.70
Purchase #3	$119.69	11.603%	$133.5776	$133.58	$133.60	$133.60
Purchase #4	$73.63	4.424%	$76.8874	$76.89	$76.90	$76.90
Purchase #5	$89.37	3.496%	$92.4944	$92.49	$92.50	$92.50
Purchase #6	$96.92	7.538%	$104.2258	$104.23	$104.25	$104.20
Purchase #7	$106.36	10.565%	$117.5969	$117.60	$117.60	$117.60
7 purchase totals =	$686.71		$751.3011	$751.31	$751.35	$751.40