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	$94.82	9.785%	$104.0981	$104.10	$104.10	$104.10
Purchase #2	$180.45	8.513%	$195.8117	$195.81	$195.80	$195.80
Purchase #3	$99.87	12.559%	$112.4127	$112.41	$112.40	$112.40
Purchase #4	$54.78	12.752%	$61.7655	$61.77	$61.75	$61.80
Purchase #5	$222.47	3.275%	$229.7559	$229.76	$229.75	$229.80
Purchase #6	$203.75	5.793%	$215.5532	$215.55	$215.55	$215.60
Purchase #7	$89.62	13.743%	$101.9365	$101.94	$101.95	$101.90
7 purchase totals =	$945.76		$1,021.3336	$1,021.34	$1,021.30	$1,021.40