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	$123.27	10.350%	$136.0284	$136.03	$136.05	$136.00
Purchase #2	$45.53	11.192%	$50.6257	$50.63	$50.65	$50.60
Purchase #3	$40.47	11.765%	$45.2313	$45.23	$45.25	$45.20
Purchase #4	$246.36	13.445%	$279.4831	$279.48	$279.50	$279.50
Purchase #5	$85.46	7.321%	$91.7165	$91.72	$91.70	$91.70
Purchase #6	$122.50	11.370%	$136.4283	$136.43	$136.45	$136.40
Purchase #7	$231.54	5.368%	$243.9691	$243.97	$243.95	$244.00
7 purchase totals =	$895.13		$983.4824	$983.49	$983.55	$983.40