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	$202.65	9.682%	$222.2706	$222.27	$222.25	$222.30
Purchase #2	$234.36	8.152%	$253.465	$253.47	$253.45	$253.50
Purchase #3	$17.90	13.140%	$20.2521	$20.25	$20.25	$20.30
Purchase #4	$79.39	4.137%	$82.6744	$82.67	$82.65	$82.70
Purchase #5	$116.96	8.629%	$127.0525	$127.05	$127.05	$127.10
Purchase #6	$194.53	12.753%	$219.3384	$219.34	$219.35	$219.30
Purchase #7	$102.59	10.197%	$113.0511	$113.05	$113.05	$113.10
7 purchase totals =	$948.38		$1,038.1041	$1,038.10	$1,038.05	$1,038.30