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	$215.43	6.510%	$229.4545	$229.45	$229.45	$229.50
Purchase #2	$42.56	7.871%	$45.9099	$45.91	$45.90	$45.90
Purchase #3	$48.96	6.677%	$52.2291	$52.23	$52.25	$52.20
Purchase #4	$240.69	3.682%	$249.5522	$249.55	$249.55	$249.60
Purchase #5	$117.76	5.225%	$123.913	$123.91	$123.90	$123.90
Purchase #6	$150.45	12.851%	$169.7843	$169.78	$169.80	$169.80
Purchase #7	$57.30	5.294%	$60.3335	$60.33	$60.35	$60.30
7 purchase totals =	$873.15		$931.1765	$931.16	$931.20	$931.20