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	$85.48	4.258%	$89.1197	$89.12	$89.10	$89.10
Purchase #2	$65.93	9.562%	$72.2342	$72.23	$72.25	$72.20
Purchase #3	$59.94	4.461%	$62.6139	$62.61	$62.60	$62.60
Purchase #4	$125.57	6.546%	$133.7898	$133.79	$133.80	$133.80
Purchase #5	$221.45	7.454%	$237.9569	$237.96	$237.95	$238.00
Purchase #6	$80.48	11.153%	$89.4559	$89.46	$89.45	$89.50
Purchase #7	$179.91	12.220%	$201.895	$201.90	$201.90	$201.90
7 purchase totals =	$818.76		$887.0654	$887.07	$887.05	$887.10