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	$71.86	6.700%	$76.6746	$76.67	$76.65	$76.70
Purchase #2	$94.84	10.672%	$104.9613	$104.96	$104.95	$105.00
Purchase #3	$189.50	11.609%	$211.4991	$211.50	$211.50	$211.50
Purchase #4	$161.56	6.354%	$171.8255	$171.83	$171.85	$171.80
Purchase #5	$79.68	12.592%	$89.7133	$89.71	$89.70	$89.70
Purchase #6	$38.84	5.607%	$41.0178	$41.02	$41.00	$41.00
Purchase #7	$89.87	11.153%	$99.8932	$99.89	$99.90	$99.90
7 purchase totals =	$726.15		$795.5848	$795.58	$795.55	$795.60