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	$33.90	10.790%	$37.5578	$37.56	$37.55	$37.60
Purchase #2	$176.48	7.345%	$189.4425	$189.44	$189.45	$189.40
Purchase #3	$239.57	9.227%	$261.6751	$261.68	$261.70	$261.70
Purchase #4	$17.34	7.214%	$18.5909	$18.59	$18.60	$18.60
Purchase #5	$246.40	4.820%	$258.2765	$258.28	$258.30	$258.30
Purchase #6	$211.26	5.312%	$222.4821	$222.48	$222.50	$222.50
Purchase #7	$206.47	13.635%	$234.6222	$234.62	$234.60	$234.60
7 purchase totals =	$1,131.42		$1,222.6471	$1,222.65	$1,222.70	$1,222.70