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	$81.94	10.239%	$90.3298	$90.33	$90.35	$90.30
Purchase #2	$129.53	12.822%	$146.1383	$146.14	$146.15	$146.10
Purchase #3	$197.72	11.418%	$220.2957	$220.30	$220.30	$220.30
Purchase #4	$201.71	10.785%	$223.4644	$223.46	$223.45	$223.50
Purchase #5	$42.37	7.765%	$45.66	$45.66	$45.65	$45.70
Purchase #6	$135.89	11.829%	$151.9644	$151.96	$151.95	$152.00
Purchase #7	$26.38	3.735%	$27.3653	$27.37	$27.35	$27.40
7 purchase totals =	$815.54		$905.2179	$905.22	$905.20	$905.30