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	$33.72	4.725%	$35.3133	$35.31	$35.30	$35.30
Purchase #2	$206.89	6.350%	$220.0275	$220.03	$220.05	$220.00
Purchase #3	$180.30	8.744%	$196.0654	$196.07	$196.05	$196.10
Purchase #4	$128.86	7.280%	$138.241	$138.24	$138.25	$138.20
Purchase #5	$188.35	4.402%	$196.6412	$196.64	$196.65	$196.60
Purchase #6	$120.62	3.128%	$124.393	$124.39	$124.40	$124.40
Purchase #7	$107.57	3.323%	$111.1446	$111.14	$111.15	$111.10
7 purchase totals =	$966.31		$1,021.8260	$1,021.82	$1,021.85	$1,021.70