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	$19.46	12.395%	$21.8721	$21.87	$21.85	$21.90
Purchase #2	$91.93	12.506%	$103.4268	$103.43	$103.45	$103.40
Purchase #3	$214.27	4.228%	$223.3293	$223.33	$223.35	$223.30
Purchase #4	$165.92	9.863%	$182.2847	$182.28	$182.30	$182.30
Purchase #5	$51.45	9.777%	$56.4803	$56.48	$56.50	$56.50
Purchase #6	$169.77	6.640%	$181.0427	$181.04	$181.05	$181.00
Purchase #7	$214.73	13.787%	$244.3348	$244.33	$244.35	$244.30
7 purchase totals =	$927.53		$1,012.7707	$1,012.76	$1,012.85	$1,012.70