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	$85.65	8.371%	$92.8198	$92.82	$92.80	$92.80
Purchase #2	$161.88	3.825%	$168.0719	$168.07	$168.05	$168.10
Purchase #3	$55.77	7.111%	$59.7358	$59.74	$59.75	$59.70
Purchase #4	$45.76	13.127%	$51.7669	$51.77	$51.75	$51.80
Purchase #5	$123.26	6.732%	$131.5579	$131.56	$131.55	$131.60
Purchase #6	$61.43	7.207%	$65.8573	$65.86	$65.85	$65.90
Purchase #7	$122.88	6.517%	$130.8881	$130.89	$130.90	$130.90
7 purchase totals =	$656.63		$700.6977	$700.71	$700.65	$700.80