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	$250.28	8.254%	$270.9381	$270.94	$270.95	$270.90
Purchase #2	$35.80	4.175%	$37.2947	$37.29	$37.30	$37.30
Purchase #3	$125.79	11.744%	$140.5628	$140.56	$140.55	$140.60
Purchase #4	$111.93	11.165%	$124.427	$124.43	$124.45	$124.40
Purchase #5	$63.91	3.501%	$66.1475	$66.15	$66.15	$66.10
Purchase #6	$175.91	7.849%	$189.7172	$189.72	$189.70	$189.70
Purchase #7	$78.68	4.845%	$82.492	$82.49	$82.50	$82.50
7 purchase totals =	$842.30		$911.5793	$911.58	$911.60	$911.50