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	$147.41	6.200%	$156.5494	$156.55	$156.55	$156.50
Purchase #2	$144.89	12.373%	$162.8172	$162.82	$162.80	$162.80
Purchase #3	$39.60	10.155%	$43.6214	$43.62	$43.60	$43.60
Purchase #4	$101.56	9.170%	$110.8731	$110.87	$110.85	$110.90
Purchase #5	$151.27	9.698%	$165.9402	$165.94	$165.95	$165.90
Purchase #6	$165.92	7.861%	$178.963	$178.96	$178.95	$179.00
Purchase #7	$119.69	9.801%	$131.4208	$131.42	$131.40	$131.40
7 purchase totals =	$870.34		$950.1851	$950.18	$950.10	$950.10