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	$12.41	8.449%	$13.4585	$13.46	$13.45	$13.50
Purchase #2	$90.62	10.227%	$99.8877	$99.89	$99.90	$99.90
Purchase #3	$25.45	6.646%	$27.1414	$27.14	$27.15	$27.10
Purchase #4	$147.40	12.266%	$165.4801	$165.48	$165.50	$165.50
Purchase #5	$186.94	8.807%	$203.4038	$203.40	$203.40	$203.40
Purchase #6	$247.73	7.200%	$265.5666	$265.57	$265.55	$265.60
Purchase #7	$48.75	5.636%	$51.4976	$51.50	$51.50	$51.50
7 purchase totals =	$759.30		$826.4357	$826.44	$826.45	$826.50