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	$94.63	11.276%	$105.3005	$105.30	$105.30	$105.30
Purchase #2	$156.43	9.507%	$171.3018	$171.30	$171.30	$171.30
Purchase #3	$43.71	10.232%	$48.1824	$48.18	$48.20	$48.20
Purchase #4	$89.56	10.231%	$98.7229	$98.72	$98.70	$98.70
Purchase #5	$113.64	12.340%	$127.6632	$127.66	$127.65	$127.70
Purchase #6	$182.41	8.806%	$198.473	$198.47	$198.45	$198.50
Purchase #7	$119.84	8.666%	$130.2253	$130.23	$130.25	$130.20
7 purchase totals =	$800.22		$879.8691	$879.86	$879.85	$879.90