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	$107.98	6.707%	$115.2222	$115.22	$115.20	$115.20
Purchase #2	$76.92	10.392%	$84.9135	$84.91	$84.90	$84.90
Purchase #3	$99.41	6.229%	$105.6022	$105.60	$105.60	$105.60
Purchase #4	$73.56	6.309%	$78.2009	$78.20	$78.20	$78.20
Purchase #5	$185.60	13.219%	$210.1345	$210.13	$210.15	$210.10
Purchase #6	$136.96	10.170%	$150.8888	$150.89	$150.90	$150.90
Purchase #7	$93.91	11.517%	$104.7256	$104.73	$104.75	$104.70
7 purchase totals =	$774.34		$849.6877	$849.68	$849.70	$849.60