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	$39.98	11.376%	$44.5281	$44.53	$44.55	$44.50
Purchase #2	$67.41	6.165%	$71.5658	$71.57	$71.55	$71.60
Purchase #3	$83.37	7.369%	$89.5135	$89.51	$89.50	$89.50
Purchase #4	$250.58	7.196%	$268.6117	$268.61	$268.60	$268.60
Purchase #5	$238.86	6.865%	$255.2577	$255.26	$255.25	$255.30
Purchase #6	$28.47	8.124%	$30.7829	$30.78	$30.80	$30.80
Purchase #7	$21.55	4.504%	$22.5206	$22.52	$22.50	$22.50
7 purchase totals =	$730.22		$782.7803	$782.78	$782.75	$782.80