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	$178.73	5.611%	$188.7585	$188.76	$188.75	$188.80
Purchase #2	$80.25	3.345%	$82.9344	$82.93	$82.95	$82.90
Purchase #3	$167.33	12.185%	$187.7192	$187.72	$187.70	$187.70
Purchase #4	$128.40	9.278%	$140.313	$140.31	$140.30	$140.30
Purchase #5	$46.53	7.814%	$50.1659	$50.17	$50.15	$50.20
Purchase #6	$10.25	6.245%	$10.8901	$10.89	$10.90	$10.90
Purchase #7	$114.59	7.564%	$123.2576	$123.26	$123.25	$123.30
7 purchase totals =	$726.08		$784.0387	$784.04	$784.00	$784.10