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	$199.71	3.366%	$206.4322	$206.43	$206.45	$206.40
Purchase #2	$127.31	9.470%	$139.3663	$139.37	$139.35	$139.40
Purchase #3	$98.44	11.450%	$109.7114	$109.71	$109.70	$109.70
Purchase #4	$200.74	6.292%	$213.3706	$213.37	$213.35	$213.40
Purchase #5	$86.34	4.404%	$90.1424	$90.14	$90.15	$90.10
Purchase #6	$72.98	8.430%	$79.1322	$79.13	$79.15	$79.10
Purchase #7	$77.67	6.753%	$82.9151	$82.92	$82.90	$82.90
7 purchase totals =	$863.19		$921.0702	$921.07	$921.05	$921.00