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	$180.46	4.122%	$187.8986	$187.90	$187.90	$187.90
Purchase #2	$49.80	8.119%	$53.8433	$53.84	$53.85	$53.80
Purchase #3	$115.48	7.429%	$124.059	$124.06	$124.05	$124.10
Purchase #4	$30.34	9.743%	$33.296	$33.30	$33.30	$33.30
Purchase #5	$172.89	13.299%	$195.8826	$195.88	$195.90	$195.90
Purchase #6	$90.90	4.120%	$94.6451	$94.65	$94.65	$94.60
Purchase #7	$159.82	13.504%	$181.4021	$181.40	$181.40	$181.40
7 purchase totals =	$799.69		$871.0267	$871.03	$871.05	$871.00