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	$125.53	9.297%	$137.2005	$137.20	$137.20	$137.20
Purchase #2	$120.99	11.377%	$134.755	$134.76	$134.75	$134.80
Purchase #3	$221.52	12.748%	$249.7594	$249.76	$249.75	$249.80
Purchase #4	$69.95	10.822%	$77.52	$77.52	$77.50	$77.50
Purchase #5	$142.61	6.789%	$152.2918	$152.29	$152.30	$152.30
Purchase #6	$109.73	3.259%	$113.3061	$113.31	$113.30	$113.30
Purchase #7	$115.78	13.577%	$131.4995	$131.50	$131.50	$131.50
7 purchase totals =	$906.11		$996.3323	$996.34	$996.30	$996.40