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	$129.90	9.690%	$142.4873	$142.49	$142.50	$142.50
Purchase #2	$70.52	13.610%	$80.1178	$80.12	$80.10	$80.10
Purchase #3	$114.90	8.546%	$124.7194	$124.72	$124.70	$124.70
Purchase #4	$68.69	13.819%	$78.1823	$78.18	$78.20	$78.20
Purchase #5	$120.49	7.221%	$129.1906	$129.19	$129.20	$129.20
Purchase #6	$125.48	4.837%	$131.5495	$131.55	$131.55	$131.50
Purchase #7	$72.76	8.168%	$78.703	$78.70	$78.70	$78.70
7 purchase totals =	$702.74		$764.9499	$764.95	$764.95	$764.90