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	$78.31	6.551%	$83.4401	$83.44	$83.45	$83.40
Purchase #2	$76.43	4.250%	$79.6783	$79.68	$79.70	$79.70
Purchase #3	$136.79	4.206%	$142.5434	$142.54	$142.55	$142.50
Purchase #4	$143.98	3.234%	$148.6363	$148.64	$148.65	$148.60
Purchase #5	$31.36	3.821%	$32.5583	$32.56	$32.55	$32.60
Purchase #6	$33.33	6.548%	$35.5124	$35.51	$35.50	$35.50
Purchase #7	$61.61	9.319%	$67.3514	$67.35	$67.35	$67.40
7 purchase totals =	$561.81		$589.7202	$589.72	$589.75	$589.70