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	$85.66	7.697%	$92.2533	$92.25	$92.25	$92.30
Purchase #2	$42.27	8.591%	$45.9014	$45.90	$45.90	$45.90
Purchase #3	$237.29	8.790%	$258.1478	$258.15	$258.15	$258.10
Purchase #4	$134.25	5.573%	$141.7318	$141.73	$141.75	$141.70
Purchase #5	$79.34	13.157%	$89.7788	$89.78	$89.80	$89.80
Purchase #6	$175.83	7.387%	$188.8186	$188.82	$188.80	$188.80
Purchase #7	$67.68	8.255%	$73.267	$73.27	$73.25	$73.30
7 purchase totals =	$822.32		$889.8987	$889.90	$889.90	$889.90