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	$78.56	13.471%	$89.1428	$89.14	$89.15	$89.10
Purchase #2	$168.91	9.134%	$184.3382	$184.34	$184.35	$184.30
Purchase #3	$56.89	8.772%	$61.8804	$61.88	$61.90	$61.90
Purchase #4	$202.57	9.767%	$222.355	$222.36	$222.35	$222.40
Purchase #5	$110.30	4.169%	$114.8984	$114.90	$114.90	$114.90
Purchase #6	$224.36	4.455%	$234.3552	$234.36	$234.35	$234.40
Purchase #7	$230.29	10.260%	$253.9178	$253.92	$253.90	$253.90
7 purchase totals =	$1,071.88		$1,160.8878	$1,160.90	$1,160.90	$1,160.90