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	$164.74	3.740%	$170.9013	$170.90	$170.90	$170.90
Purchase #2	$31.83	4.800%	$33.3578	$33.36	$33.35	$33.40
Purchase #3	$82.28	11.340%	$91.6106	$91.61	$91.60	$91.60
Purchase #4	$73.96	12.729%	$83.3744	$83.37	$83.35	$83.40
Purchase #5	$158.81	7.873%	$171.3131	$171.31	$171.30	$171.30
Purchase #6	$118.33	13.490%	$134.2927	$134.29	$134.30	$134.30
Purchase #7	$228.98	12.499%	$257.6002	$257.60	$257.60	$257.60
7 purchase totals =	$858.93		$942.4501	$942.44	$942.40	$942.50