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	$46.77	11.753%	$52.2669	$52.27	$52.25	$52.30
Purchase #2	$127.39	13.292%	$144.3227	$144.32	$144.30	$144.30
Purchase #3	$140.98	8.343%	$152.742	$152.74	$152.75	$152.70
Purchase #4	$180.94	7.524%	$194.5539	$194.55	$194.55	$194.60
Purchase #5	$51.32	7.710%	$55.2768	$55.28	$55.30	$55.30
Purchase #6	$246.27	3.287%	$254.3649	$254.36	$254.35	$254.40
Purchase #7	$245.76	12.248%	$275.8607	$275.86	$275.85	$275.90
7 purchase totals =	$1,039.43		$1,129.3879	$1,129.38	$1,129.35	$1,129.50