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	$51.75	11.152%	$57.5212	$57.52	$57.50	$57.50
Purchase #2	$87.52	10.620%	$96.8146	$96.81	$96.80	$96.80
Purchase #3	$53.33	7.317%	$57.2322	$57.23	$57.25	$57.20
Purchase #4	$53.86	3.713%	$55.8598	$55.86	$55.85	$55.90
Purchase #5	$181.27	13.822%	$206.3251	$206.33	$206.35	$206.30
Purchase #6	$158.66	8.258%	$171.7621	$171.76	$171.75	$171.80
Purchase #7	$247.79	13.620%	$281.539	$281.54	$281.55	$281.50
7 purchase totals =	$834.18		$927.0540	$927.05	$927.05	$927.00