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	$87.83	3.802%	$91.1693	$91.17	$91.15	$91.20
Purchase #2	$165.43	12.290%	$185.7613	$185.76	$185.75	$185.80
Purchase #3	$65.34	9.172%	$71.333	$71.33	$71.35	$71.30
Purchase #4	$228.88	6.546%	$243.8625	$243.86	$243.85	$243.90
Purchase #5	$14.65	8.127%	$15.8406	$15.84	$15.85	$15.80
Purchase #6	$89.52	9.334%	$97.8758	$97.88	$97.90	$97.90
Purchase #7	$115.64	13.397%	$131.1323	$131.13	$131.15	$131.10
7 purchase totals =	$767.29		$836.9748	$836.97	$837.00	$837.00