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	$72.67	11.666%	$81.1477	$81.15	$81.15	$81.10
Purchase #2	$186.84	7.419%	$200.7017	$200.70	$200.70	$200.70
Purchase #3	$221.79	6.453%	$236.1021	$236.10	$236.10	$236.10
Purchase #4	$250.46	10.545%	$276.871	$276.87	$276.85	$276.90
Purchase #5	$212.34	12.515%	$238.9144	$238.91	$238.90	$238.90
Purchase #6	$156.82	13.759%	$178.3969	$178.40	$178.40	$178.40
Purchase #7	$120.87	5.747%	$127.8164	$127.82	$127.80	$127.80
7 purchase totals =	$1,221.79		$1,339.9502	$1,339.95	$1,339.90	$1,339.90