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	$245.48	10.635%	$271.5868	$271.59	$271.60	$271.60
Purchase #2	$179.33	9.691%	$196.7089	$196.71	$196.70	$196.70
Purchase #3	$79.69	3.550%	$82.519	$82.52	$82.50	$82.50
Purchase #4	$147.35	9.684%	$161.6194	$161.62	$161.60	$161.60
Purchase #5	$125.99	12.364%	$141.5674	$141.57	$141.55	$141.60
Purchase #6	$102.82	3.460%	$106.3776	$106.38	$106.40	$106.40
Purchase #7	$57.30	9.759%	$62.8919	$62.89	$62.90	$62.90
7 purchase totals =	$937.96		$1,023.2710	$1,023.28	$1,023.25	$1,023.30