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	$120.69	13.498%	$136.9807	$136.98	$137.00	$137.00
Purchase #2	$82.85	9.174%	$90.4507	$90.45	$90.45	$90.50
Purchase #3	$169.74	10.849%	$188.1551	$188.16	$188.15	$188.20
Purchase #4	$17.73	13.489%	$20.1216	$20.12	$20.10	$20.10
Purchase #5	$41.61	9.146%	$45.4157	$45.42	$45.40	$45.40
Purchase #6	$236.46	4.646%	$247.4459	$247.45	$247.45	$247.40
Purchase #7	$197.61	7.585%	$212.5987	$212.60	$212.60	$212.60
7 purchase totals =	$866.69		$941.1684	$941.18	$941.15	$941.20