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	$211.27	13.740%	$240.2985	$240.30	$240.30	$240.30
Purchase #2	$222.65	3.239%	$229.8616	$229.86	$229.85	$229.90
Purchase #3	$83.50	3.187%	$86.1611	$86.16	$86.15	$86.20
Purchase #4	$184.96	13.860%	$210.5955	$210.60	$210.60	$210.60
Purchase #5	$112.33	7.191%	$120.4077	$120.41	$120.40	$120.40
Purchase #6	$26.66	6.317%	$28.3441	$28.34	$28.35	$28.30
Purchase #7	$113.49	11.807%	$126.8898	$126.89	$126.90	$126.90
7 purchase totals =	$954.86		$1,042.5583	$1,042.56	$1,042.55	$1,042.60