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	$188.90	6.322%	$200.8423	$200.84	$200.85	$200.80
Purchase #2	$135.47	9.847%	$148.8097	$148.81	$148.80	$148.80
Purchase #3	$78.95	11.428%	$87.9724	$87.97	$87.95	$88.00
Purchase #4	$138.49	4.568%	$144.8162	$144.82	$144.80	$144.80
Purchase #5	$238.59	12.588%	$268.6237	$268.62	$268.60	$268.60
Purchase #6	$218.79	11.300%	$243.5133	$243.51	$243.50	$243.50
Purchase #7	$47.98	5.304%	$50.5249	$50.52	$50.50	$50.50
7 purchase totals =	$1,047.17		$1,145.1025	$1,145.09	$1,145.00	$1,145.00