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	$87.78	4.337%	$91.587	$91.59	$91.60	$91.60
Purchase #2	$226.61	7.787%	$244.2561	$244.26	$244.25	$244.30
Purchase #3	$175.39	6.492%	$186.7763	$186.78	$186.80	$186.80
Purchase #4	$195.78	7.616%	$210.6906	$210.69	$210.70	$210.70
Purchase #5	$233.94	10.821%	$259.2546	$259.25	$259.25	$259.30
Purchase #6	$81.79	6.560%	$87.1554	$87.16	$87.15	$87.20
Purchase #7	$178.30	12.607%	$200.7783	$200.78	$200.80	$200.80
7 purchase totals =	$1,179.59		$1,280.4983	$1,280.51	$1,280.55	$1,280.70