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	$157.33	4.539%	$164.4712	$164.47	$164.45	$164.50
Purchase #2	$61.98	5.859%	$65.6114	$65.61	$65.60	$65.60
Purchase #3	$143.79	4.652%	$150.4791	$150.48	$150.50	$150.50
Purchase #4	$143.72	3.430%	$148.6496	$148.65	$148.65	$148.60
Purchase #5	$192.27	12.525%	$216.3518	$216.35	$216.35	$216.40
Purchase #6	$38.34	7.711%	$41.2964	$41.30	$41.30	$41.30
Purchase #7	$81.58	4.807%	$85.5016	$85.50	$85.50	$85.50
7 purchase totals =	$819.01		$872.3611	$872.36	$872.35	$872.40