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	$42.93	10.711%	$47.5282	$47.53	$47.55	$47.50
Purchase #2	$85.66	3.150%	$88.3583	$88.36	$88.35	$88.40
Purchase #3	$209.82	12.838%	$236.7567	$236.76	$236.75	$236.80
Purchase #4	$239.47	11.838%	$267.8185	$267.82	$267.80	$267.80
Purchase #5	$71.48	3.279%	$73.8238	$73.82	$73.80	$73.80
Purchase #6	$34.60	10.199%	$38.1289	$38.13	$38.15	$38.10
Purchase #7	$89.65	10.731%	$99.2703	$99.27	$99.25	$99.30
7 purchase totals =	$773.61		$851.6847	$851.69	$851.65	$851.70