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	$8.70	13.786%	$9.8994	$9.90	$9.90	$9.90
Purchase #2	$111.55	12.564%	$125.5651	$125.57	$125.55	$125.60
Purchase #3	$153.94	7.263%	$165.1207	$165.12	$165.10	$165.10
Purchase #4	$90.39	11.441%	$100.7315	$100.73	$100.75	$100.70
Purchase #5	$145.83	12.469%	$164.0135	$164.01	$164.00	$164.00
Purchase #6	$35.48	4.383%	$37.0351	$37.04	$37.05	$37.00
Purchase #7	$168.51	12.616%	$189.7692	$189.77	$189.75	$189.80
7 purchase totals =	$714.40		$792.1345	$792.14	$792.10	$792.10