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	$69.25	12.474%	$77.8882	$77.89	$77.90	$77.90
Purchase #2	$40.97	11.636%	$45.7373	$45.74	$45.75	$45.70
Purchase #3	$238.46	12.584%	$268.4678	$268.47	$268.45	$268.50
Purchase #4	$76.46	3.263%	$78.9549	$78.95	$78.95	$79.00
Purchase #5	$213.27	5.755%	$225.5437	$225.54	$225.55	$225.50
Purchase #6	$167.37	3.459%	$173.1593	$173.16	$173.15	$173.20
Purchase #7	$116.83	12.752%	$131.7282	$131.73	$131.75	$131.70
7 purchase totals =	$922.61		$1,001.4794	$1,001.48	$1,001.50	$1,001.50