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	$83.86	6.411%	$89.2363	$89.24	$89.25	$89.20
Purchase #2	$221.25	6.279%	$235.1423	$235.14	$235.15	$235.10
Purchase #3	$167.83	13.701%	$190.8244	$190.82	$190.80	$190.80
Purchase #4	$78.51	9.806%	$86.2087	$86.21	$86.20	$86.20
Purchase #5	$46.77	3.847%	$48.5692	$48.57	$48.55	$48.60
Purchase #6	$85.46	3.432%	$88.393	$88.39	$88.40	$88.40
Purchase #7	$28.47	3.661%	$29.5123	$29.51	$29.50	$29.50
7 purchase totals =	$712.15		$767.8862	$767.88	$767.85	$767.80