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	$249.82	12.524%	$281.1075	$281.11	$281.10	$281.10
Purchase #2	$117.46	9.765%	$128.93	$128.93	$128.95	$128.90
Purchase #3	$155.68	6.330%	$165.5345	$165.53	$165.55	$165.50
Purchase #4	$71.27	13.774%	$81.0867	$81.09	$81.10	$81.10
Purchase #5	$68.73	12.437%	$77.278	$77.28	$77.30	$77.30
Purchase #6	$59.39	9.456%	$65.0059	$65.01	$65.00	$65.00
Purchase #7	$233.33	7.547%	$250.9394	$250.94	$250.95	$250.90
7 purchase totals =	$955.68		$1,049.8820	$1,049.89	$1,049.95	$1,049.80