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	$211.64	9.578%	$231.9109	$231.91	$231.90	$231.90
Purchase #2	$242.84	11.304%	$270.2906	$270.29	$270.30	$270.30
Purchase #3	$99.59	6.508%	$106.0713	$106.07	$106.05	$106.10
Purchase #4	$135.31	9.689%	$148.4202	$148.42	$148.40	$148.40
Purchase #5	$48.61	9.230%	$53.0967	$53.10	$53.10	$53.10
Purchase #6	$63.57	13.343%	$72.0521	$72.05	$72.05	$72.10
Purchase #7	$205.49	6.202%	$218.2345	$218.23	$218.25	$218.20
7 purchase totals =	$1,007.05		$1,100.0763	$1,100.07	$1,100.05	$1,100.10