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	$237.57	5.359%	$250.3014	$250.30	$250.30	$250.30
Purchase #2	$40.70	3.461%	$42.1086	$42.11	$42.10	$42.10
Purchase #3	$110.49	11.714%	$123.4328	$123.43	$123.45	$123.40
Purchase #4	$90.86	9.833%	$99.7943	$99.79	$99.80	$99.80
Purchase #5	$90.28	12.795%	$101.8313	$101.83	$101.85	$101.80
Purchase #6	$91.93	5.644%	$97.1185	$97.12	$97.10	$97.10
Purchase #7	$146.80	12.366%	$164.9533	$164.95	$164.95	$165.00
7 purchase totals =	$808.63		$879.5402	$879.53	$879.55	$879.50