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	$41.92	7.774%	$45.1789	$45.18	$45.20	$45.20
Purchase #2	$106.64	8.358%	$115.553	$115.55	$115.55	$115.60
Purchase #3	$56.68	5.245%	$59.6529	$59.65	$59.65	$59.70
Purchase #4	$41.85	7.821%	$45.1231	$45.12	$45.10	$45.10
Purchase #5	$42.34	5.142%	$44.5171	$44.52	$44.50	$44.50
Purchase #6	$115.96	10.667%	$128.3295	$128.33	$128.35	$128.30
Purchase #7	$204.34	5.480%	$215.5378	$215.54	$215.55	$215.50
7 purchase totals =	$609.73		$653.8923	$653.89	$653.90	$653.90