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	$88.42	3.354%	$91.3856	$91.39	$91.40	$91.40
Purchase #2	$244.86	11.588%	$273.2344	$273.23	$273.25	$273.20
Purchase #3	$190.91	7.656%	$205.5261	$205.53	$205.55	$205.50
Purchase #4	$82.32	3.638%	$85.3148	$85.31	$85.30	$85.30
Purchase #5	$83.83	9.177%	$91.5231	$91.52	$91.50	$91.50
Purchase #6	$7.64	8.219%	$8.2679	$8.27	$8.25	$8.30
Purchase #7	$34.71	3.343%	$35.8704	$35.87	$35.85	$35.90
7 purchase totals =	$732.69		$791.1223	$791.12	$791.10	$791.10