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	$12.55	7.363%	$13.4741	$13.47	$13.45	$13.50
Purchase #2	$179.43	13.321%	$203.3319	$203.33	$203.35	$203.30
Purchase #3	$71.77	11.310%	$79.8872	$79.89	$79.90	$79.90
Purchase #4	$247.28	10.357%	$272.8908	$272.89	$272.90	$272.90
Purchase #5	$77.32	6.679%	$82.4842	$82.48	$82.50	$82.50
Purchase #6	$158.76	7.229%	$170.2368	$170.24	$170.25	$170.20
Purchase #7	$184.59	7.850%	$199.0803	$199.08	$199.10	$199.10
7 purchase totals =	$931.70		$1,021.3853	$1,021.38	$1,021.45	$1,021.40