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	$81.63	6.224%	$86.7107	$86.71	$86.70	$86.70
Purchase #2	$48.61	6.841%	$51.9354	$51.94	$51.95	$51.90
Purchase #3	$32.88	5.107%	$34.5592	$34.56	$34.55	$34.60
Purchase #4	$119.62	4.364%	$124.8402	$124.84	$124.85	$124.80
Purchase #5	$247.90	6.303%	$263.5251	$263.53	$263.55	$263.50
Purchase #6	$184.36	6.443%	$196.2383	$196.24	$196.25	$196.20
Purchase #7	$30.89	10.254%	$34.0575	$34.06	$34.05	$34.10
7 purchase totals =	$745.89		$791.8664	$791.88	$791.90	$791.80