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	$50.88	3.648%	$52.7361	$52.74	$52.75	$52.70
Purchase #2	$168.98	11.764%	$188.8588	$188.86	$188.85	$188.90
Purchase #3	$72.56	10.397%	$80.1041	$80.10	$80.10	$80.10
Purchase #4	$209.33	6.715%	$223.3865	$223.39	$223.40	$223.40
Purchase #5	$186.34	9.121%	$203.3361	$203.34	$203.35	$203.30
Purchase #6	$82.82	3.205%	$85.4744	$85.47	$85.45	$85.50
Purchase #7	$107.28	7.678%	$115.517	$115.52	$115.50	$115.50
7 purchase totals =	$878.19		$949.4130	$949.42	$949.40	$949.40