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	$37.66	8.704%	$40.9379	$40.94	$40.95	$40.90
Purchase #2	$175.39	10.768%	$194.276	$194.28	$194.30	$194.30
Purchase #3	$171.38	11.615%	$191.2858	$191.29	$191.30	$191.30
Purchase #4	$44.74	11.515%	$49.8918	$49.89	$49.90	$49.90
Purchase #5	$66.85	10.488%	$73.8612	$73.86	$73.85	$73.90
Purchase #6	$67.35	7.201%	$72.1999	$72.20	$72.20	$72.20
Purchase #7	$165.39	6.153%	$175.5664	$175.57	$175.55	$175.60
7 purchase totals =	$728.76		$798.0190	$798.03	$798.05	$798.10