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	$66.58	6.828%	$71.1261	$71.13	$71.15	$71.10
Purchase #2	$33.25	5.784%	$35.1732	$35.17	$35.15	$35.20
Purchase #3	$148.80	11.212%	$165.4835	$165.48	$165.50	$165.50
Purchase #4	$147.55	11.356%	$164.3058	$164.31	$164.30	$164.30
Purchase #5	$48.74	11.290%	$54.2427	$54.24	$54.25	$54.20
Purchase #6	$209.45	5.296%	$220.5425	$220.54	$220.55	$220.50
Purchase #7	$136.70	11.557%	$152.4984	$152.50	$152.50	$152.50
7 purchase totals =	$791.07		$863.3722	$863.37	$863.40	$863.30