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	$79.38	3.830%	$82.4203	$82.42	$82.40	$82.40
Purchase #2	$71.33	8.102%	$77.1092	$77.11	$77.10	$77.10
Purchase #3	$239.51	10.294%	$264.1652	$264.17	$264.15	$264.20
Purchase #4	$47.85	11.516%	$53.3604	$53.36	$53.35	$53.40
Purchase #5	$73.95	13.221%	$83.7269	$83.73	$83.75	$83.70
Purchase #6	$36.49	10.452%	$40.3039	$40.30	$40.30	$40.30
Purchase #7	$158.35	12.701%	$178.462	$178.46	$178.45	$178.50
7 purchase totals =	$706.86		$779.5479	$779.55	$779.50	$779.60