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	$136.89	6.145%	$145.3019	$145.30	$145.30	$145.30
Purchase #2	$72.48	4.354%	$75.6358	$75.64	$75.65	$75.60
Purchase #3	$91.86	7.821%	$99.0444	$99.04	$99.05	$99.00
Purchase #4	$248.98	9.473%	$272.5659	$272.57	$272.55	$272.60
Purchase #5	$6.88	3.162%	$7.0975	$7.10	$7.10	$7.10
Purchase #6	$171.77	10.740%	$190.2181	$190.22	$190.20	$190.20
Purchase #7	$190.26	12.176%	$213.4261	$213.43	$213.45	$213.40
7 purchase totals =	$919.12		$1,003.2897	$1,003.30	$1,003.30	$1,003.20