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	$56.55	5.408%	$59.6082	$59.61	$59.60	$59.60
Purchase #2	$198.89	12.131%	$223.0173	$223.02	$223.00	$223.00
Purchase #3	$93.59	11.214%	$104.0852	$104.09	$104.10	$104.10
Purchase #4	$19.60	10.321%	$21.6229	$21.62	$21.60	$21.60
Purchase #5	$79.56	12.387%	$89.4151	$89.42	$89.40	$89.40
Purchase #6	$180.53	6.279%	$191.8655	$191.87	$191.85	$191.90
Purchase #7	$207.62	4.370%	$216.693	$216.69	$216.70	$216.70
7 purchase totals =	$836.34		$906.3072	$906.32	$906.25	$906.30