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	$225.49	6.674%	$240.5392	$240.54	$240.55	$240.50
Purchase #2	$57.47	12.604%	$64.7135	$64.71	$64.70	$64.70
Purchase #3	$78.47	9.118%	$85.6249	$85.62	$85.60	$85.60
Purchase #4	$81.59	9.813%	$89.5964	$89.60	$89.60	$89.60
Purchase #5	$238.43	4.834%	$249.9557	$249.96	$249.95	$250.00
Purchase #6	$59.45	12.391%	$66.8164	$66.82	$66.80	$66.80
Purchase #7	$91.63	3.413%	$94.7573	$94.76	$94.75	$94.80
7 purchase totals =	$832.53		$892.0034	$892.01	$891.95	$892.00