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	$97.82	3.369%	$101.1156	$101.12	$101.10	$101.10
Purchase #2	$37.69	11.729%	$42.1107	$42.11	$42.10	$42.10
Purchase #3	$183.94	3.667%	$190.6851	$190.69	$190.70	$190.70
Purchase #4	$248.35	13.564%	$282.0362	$282.04	$282.05	$282.00
Purchase #5	$100.98	9.157%	$110.2267	$110.23	$110.25	$110.20
Purchase #6	$80.67	10.363%	$89.0298	$89.03	$89.05	$89.00
Purchase #7	$209.76	3.211%	$216.4954	$216.50	$216.50	$216.50
7 purchase totals =	$959.21		$1,031.6995	$1,031.72	$1,031.75	$1,031.60