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	$79.62	3.384%	$82.3143	$82.31	$82.30	$82.30
Purchase #2	$215.58	10.807%	$238.8777	$238.88	$238.90	$238.90
Purchase #3	$73.64	5.229%	$77.4906	$77.49	$77.50	$77.50
Purchase #4	$224.73	11.228%	$249.9627	$249.96	$249.95	$250.00
Purchase #5	$19.91	13.375%	$22.573	$22.57	$22.55	$22.60
Purchase #6	$80.31	11.118%	$89.2389	$89.24	$89.25	$89.20
Purchase #7	$71.25	6.108%	$75.602	$75.60	$75.60	$75.60
7 purchase totals =	$765.04		$836.0592	$836.05	$836.05	$836.10