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	$75.47	6.150%	$80.1114	$80.11	$80.10	$80.10
Purchase #2	$198.33	10.385%	$218.9266	$218.93	$218.95	$218.90
Purchase #3	$175.61	12.113%	$196.8816	$196.88	$196.90	$196.90
Purchase #4	$36.43	6.842%	$38.9225	$38.92	$38.90	$38.90
Purchase #5	$190.46	6.826%	$203.4608	$203.46	$203.45	$203.50
Purchase #6	$245.70	3.244%	$253.6705	$253.67	$253.65	$253.70
Purchase #7	$148.98	12.371%	$167.4103	$167.41	$167.40	$167.40
7 purchase totals =	$1,070.98		$1,159.3837	$1,159.38	$1,159.35	$1,159.40