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	$92.92	12.209%	$104.2646	$104.26	$104.25	$104.30
Purchase #2	$191.86	8.142%	$207.4812	$207.48	$207.50	$207.50
Purchase #3	$78.61	9.197%	$85.8398	$85.84	$85.85	$85.80
Purchase #4	$160.41	12.147%	$179.895	$179.90	$179.90	$179.90
Purchase #5	$69.91	11.542%	$77.979	$77.98	$78.00	$78.00
Purchase #6	$124.71	9.723%	$136.8356	$136.84	$136.85	$136.80
Purchase #7	$57.89	13.363%	$65.6258	$65.63	$65.65	$65.60
7 purchase totals =	$776.31		$857.9210	$857.93	$858.00	$857.90