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	$33.41	12.300%	$37.5194	$37.52	$37.50	$37.50
Purchase #2	$140.29	12.555%	$157.9034	$157.90	$157.90	$157.90
Purchase #3	$25.84	6.423%	$27.4997	$27.50	$27.50	$27.50
Purchase #4	$192.31	13.275%	$217.8392	$217.84	$217.85	$217.80
Purchase #5	$175.58	13.349%	$199.0182	$199.02	$199.00	$199.00
Purchase #6	$38.88	11.277%	$43.2645	$43.26	$43.25	$43.30
Purchase #7	$59.98	12.361%	$67.3941	$67.39	$67.40	$67.40
7 purchase totals =	$666.29		$750.4385	$750.43	$750.40	$750.40