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	$55.62	11.273%	$61.89	$61.89	$61.90	$61.90
Purchase #2	$117.58	8.112%	$127.1181	$127.12	$127.10	$127.10
Purchase #3	$113.70	9.342%	$124.3219	$124.32	$124.30	$124.30
Purchase #4	$47.86	9.399%	$52.3584	$52.36	$52.35	$52.40
Purchase #5	$219.56	11.265%	$244.2934	$244.29	$244.30	$244.30
Purchase #6	$13.88	10.473%	$15.3337	$15.33	$15.35	$15.30
Purchase #7	$31.49	12.240%	$35.3444	$35.34	$35.35	$35.30
7 purchase totals =	$599.69		$660.6599	$660.65	$660.65	$660.60