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	$52.93	12.871%	$59.7426	$59.74	$59.75	$59.70
Purchase #2	$17.69	9.737%	$19.4125	$19.41	$19.40	$19.40
Purchase #3	$152.63	4.803%	$159.9608	$159.96	$159.95	$160.00
Purchase #4	$128.95	9.524%	$141.2312	$141.23	$141.25	$141.20
Purchase #5	$211.65	3.256%	$218.5413	$218.54	$218.55	$218.50
Purchase #6	$203.96	8.785%	$221.8779	$221.88	$221.90	$221.90
Purchase #7	$42.44	7.419%	$45.5886	$45.59	$45.60	$45.60
7 purchase totals =	$810.25		$866.3549	$866.35	$866.40	$866.30