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	$72.34	12.311%	$81.2458	$81.25	$81.25	$81.20
Purchase #2	$68.66	11.793%	$76.7571	$76.76	$76.75	$76.80
Purchase #3	$80.41	12.206%	$90.2248	$90.22	$90.20	$90.20
Purchase #4	$128.52	8.506%	$139.4519	$139.45	$139.45	$139.50
Purchase #5	$179.61	6.463%	$191.2182	$191.22	$191.20	$191.20
Purchase #6	$188.60	4.701%	$197.4661	$197.47	$197.45	$197.50
Purchase #7	$216.95	12.571%	$244.2228	$244.22	$244.20	$244.20
7 purchase totals =	$935.09		$1,020.5867	$1,020.59	$1,020.50	$1,020.60