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	$89.78	11.609%	$100.2026	$100.20	$100.20	$100.20
Purchase #2	$46.95	13.331%	$53.2089	$53.21	$53.20	$53.20
Purchase #3	$146.64	13.573%	$166.5434	$166.54	$166.55	$166.50
Purchase #4	$206.47	12.196%	$231.6511	$231.65	$231.65	$231.70
Purchase #5	$88.69	12.639%	$99.8995	$99.90	$99.90	$99.90
Purchase #6	$183.48	3.289%	$189.5147	$189.51	$189.50	$189.50
Purchase #7	$77.80	9.257%	$85.0019	$85.00	$85.00	$85.00
7 purchase totals =	$839.81		$926.0221	$926.01	$926.00	$926.00