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	$89.81	7.751%	$96.7712	$96.77	$96.75	$96.80
Purchase #2	$61.32	5.630%	$64.7723	$64.77	$64.75	$64.80
Purchase #3	$136.46	12.811%	$153.9419	$153.94	$153.95	$153.90
Purchase #4	$159.46	5.401%	$168.0724	$168.07	$168.05	$168.10
Purchase #5	$108.35	7.170%	$116.1187	$116.12	$116.10	$116.10
Purchase #6	$83.37	3.636%	$86.4013	$86.40	$86.40	$86.40
Purchase #7	$80.53	4.183%	$83.8986	$83.90	$83.90	$83.90
7 purchase totals =	$719.30		$769.9764	$769.97	$769.90	$770.00