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	$238.92	8.534%	$259.3094	$259.31	$259.30	$259.30
Purchase #2	$174.35	6.281%	$185.3009	$185.30	$185.30	$185.30
Purchase #3	$141.94	10.803%	$157.2738	$157.27	$157.25	$157.30
Purchase #4	$78.46	12.689%	$88.4158	$88.42	$88.40	$88.40
Purchase #5	$110.96	11.447%	$123.6616	$123.66	$123.65	$123.70
Purchase #6	$219.50	3.809%	$227.8608	$227.86	$227.85	$227.90
Purchase #7	$242.73	11.610%	$270.911	$270.91	$270.90	$270.90
7 purchase totals =	$1,206.86		$1,312.7333	$1,312.73	$1,312.65	$1,312.80