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	$85.33	5.685%	$90.181	$90.18	$90.20	$90.20
Purchase #2	$28.69	8.280%	$31.0655	$31.07	$31.05	$31.10
Purchase #3	$63.94	11.651%	$71.3896	$71.39	$71.40	$71.40
Purchase #4	$34.75	13.344%	$39.387	$39.39	$39.40	$39.40
Purchase #5	$235.90	3.563%	$244.3051	$244.31	$244.30	$244.30
Purchase #6	$26.37	3.712%	$27.3489	$27.35	$27.35	$27.30
Purchase #7	$167.56	8.194%	$181.2899	$181.29	$181.30	$181.30
7 purchase totals =	$642.54		$684.9670	$684.98	$685.00	$685.00