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	$79.65	12.667%	$89.7393	$89.74	$89.75	$89.70
Purchase #2	$226.37	12.257%	$254.1162	$254.12	$254.10	$254.10
Purchase #3	$57.36	7.774%	$61.8192	$61.82	$61.80	$61.80
Purchase #4	$13.36	6.124%	$14.1782	$14.18	$14.20	$14.20
Purchase #5	$71.79	7.373%	$77.0831	$77.08	$77.10	$77.10
Purchase #6	$66.82	7.604%	$71.901	$71.90	$71.90	$71.90
Purchase #7	$152.47	6.800%	$162.838	$162.84	$162.85	$162.80
7 purchase totals =	$667.82		$731.6750	$731.68	$731.70	$731.60