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	$135.73	11.193%	$150.9223	$150.92	$150.90	$150.90
Purchase #2	$83.97	7.342%	$90.1351	$90.14	$90.15	$90.10
Purchase #3	$226.78	8.274%	$245.5438	$245.54	$245.55	$245.50
Purchase #4	$48.39	11.720%	$54.0613	$54.06	$54.05	$54.10
Purchase #5	$45.65	4.132%	$47.5363	$47.54	$47.55	$47.50
Purchase #6	$226.76	10.542%	$250.665	$250.67	$250.65	$250.70
Purchase #7	$26.63	8.237%	$28.8235	$28.82	$28.80	$28.80
7 purchase totals =	$793.91		$867.6873	$867.69	$867.65	$867.60