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	$216.51	11.722%	$241.8893	$241.89	$241.90	$241.90
Purchase #2	$55.30	5.143%	$58.1441	$58.14	$58.15	$58.10
Purchase #3	$204.76	12.830%	$231.0307	$231.03	$231.05	$231.00
Purchase #4	$65.96	9.706%	$72.3621	$72.36	$72.35	$72.40
Purchase #5	$76.39	9.178%	$83.4011	$83.40	$83.40	$83.40
Purchase #6	$58.56	8.809%	$63.7186	$63.72	$63.70	$63.70
Purchase #7	$39.54	6.266%	$42.0176	$42.02	$42.00	$42.00
7 purchase totals =	$717.02		$792.5635	$792.56	$792.55	$792.50