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	$218.75	11.281%	$243.4272	$243.43	$243.45	$243.40
Purchase #2	$231.90	3.634%	$240.3272	$240.33	$240.35	$240.30
Purchase #3	$90.41	12.737%	$101.9255	$101.93	$101.95	$101.90
Purchase #4	$113.34	12.742%	$127.7818	$127.78	$127.80	$127.80
Purchase #5	$77.35	4.161%	$80.5685	$80.57	$80.55	$80.60
Purchase #6	$204.54	11.368%	$227.7921	$227.79	$227.80	$227.80
Purchase #7	$53.36	4.464%	$55.742	$55.74	$55.75	$55.70
7 purchase totals =	$989.65		$1,077.5643	$1,077.57	$1,077.65	$1,077.50