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	$191.46	13.832%	$217.9427	$217.94	$217.95	$217.90
Purchase #2	$124.80	7.257%	$133.8567	$133.86	$133.85	$133.90
Purchase #3	$181.36	4.744%	$189.9637	$189.96	$189.95	$190.00
Purchase #4	$70.49	10.692%	$78.0268	$78.03	$78.05	$78.00
Purchase #5	$172.89	7.427%	$185.7305	$185.73	$185.75	$185.70
Purchase #6	$67.40	5.497%	$71.105	$71.11	$71.10	$71.10
Purchase #7	$29.34	13.612%	$33.3338	$33.33	$33.35	$33.30
7 purchase totals =	$837.74		$909.9592	$909.96	$910.00	$909.90