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	$32.78	12.312%	$36.8159	$36.82	$36.80	$36.80
Purchase #2	$85.89	3.725%	$89.0894	$89.09	$89.10	$89.10
Purchase #3	$216.42	11.165%	$240.5833	$240.58	$240.60	$240.60
Purchase #4	$64.50	4.507%	$67.407	$67.41	$67.40	$67.40
Purchase #5	$79.96	11.607%	$89.241	$89.24	$89.25	$89.20
Purchase #6	$62.52	11.852%	$69.9299	$69.93	$69.95	$69.90
Purchase #7	$184.78	3.559%	$191.3563	$191.36	$191.35	$191.40
7 purchase totals =	$726.85		$784.4228	$784.43	$784.45	$784.40