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	$80.29	12.421%	$90.2628	$90.26	$90.25	$90.30
Purchase #2	$103.53	7.488%	$111.2823	$111.28	$111.30	$111.30
Purchase #3	$102.91	7.779%	$110.9154	$110.92	$110.90	$110.90
Purchase #4	$131.27	5.834%	$138.9283	$138.93	$138.95	$138.90
Purchase #5	$70.42	10.790%	$78.0183	$78.02	$78.00	$78.00
Purchase #6	$92.49	10.655%	$102.3448	$102.34	$102.35	$102.30
Purchase #7	$210.25	10.512%	$232.3515	$232.35	$232.35	$232.40
7 purchase totals =	$791.16		$864.1034	$864.10	$864.10	$864.10