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	$189.32	8.409%	$205.2399	$205.24	$205.25	$205.20
Purchase #2	$233.76	9.264%	$255.4155	$255.42	$255.40	$255.40
Purchase #3	$100.51	8.809%	$109.3639	$109.36	$109.35	$109.40
Purchase #4	$43.51	9.571%	$47.6743	$47.67	$47.65	$47.70
Purchase #5	$32.65	7.673%	$35.1552	$35.16	$35.15	$35.20
Purchase #6	$221.55	7.498%	$238.1618	$238.16	$238.15	$238.20
Purchase #7	$29.65	12.772%	$33.4369	$33.44	$33.45	$33.40
7 purchase totals =	$850.95		$924.4475	$924.45	$924.40	$924.50