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	$223.64	3.300%	$231.0201	$231.02	$231.00	$231.00
Purchase #2	$222.55	12.260%	$249.8346	$249.83	$249.85	$249.80
Purchase #3	$215.43	11.338%	$239.8555	$239.86	$239.85	$239.90
Purchase #4	$165.75	3.398%	$171.3822	$171.38	$171.40	$171.40
Purchase #5	$243.60	8.529%	$264.3766	$264.38	$264.40	$264.40
Purchase #6	$195.87	13.603%	$222.5142	$222.51	$222.50	$222.50
Purchase #7	$38.56	11.845%	$43.1274	$43.13	$43.15	$43.10
7 purchase totals =	$1,305.40		$1,422.1106	$1,422.11	$1,422.15	$1,422.10