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	$185.30	3.326%	$191.4631	$191.46	$191.45	$191.50
Purchase #2	$81.87	3.627%	$84.8394	$84.84	$84.85	$84.80
Purchase #3	$223.98	8.716%	$243.5021	$243.50	$243.50	$243.50
Purchase #4	$64.69	11.795%	$72.3202	$72.32	$72.30	$72.30
Purchase #5	$24.46	4.296%	$25.5108	$25.51	$25.50	$25.50
Purchase #6	$69.76	7.106%	$74.7171	$74.72	$74.70	$74.70
Purchase #7	$185.50	13.683%	$210.882	$210.88	$210.90	$210.90
7 purchase totals =	$835.56		$903.2347	$903.23	$903.20	$903.20