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	$76.49	3.102%	$78.8627	$78.86	$78.85	$78.90
Purchase #2	$97.87	3.530%	$101.3248	$101.32	$101.30	$101.30
Purchase #3	$5.59	9.322%	$6.1111	$6.11	$6.10	$6.10
Purchase #4	$211.82	8.125%	$229.0304	$229.03	$229.05	$229.00
Purchase #5	$71.49	11.765%	$79.9008	$79.90	$79.90	$79.90
Purchase #6	$124.62	5.573%	$131.5651	$131.57	$131.55	$131.60
Purchase #7	$78.96	8.157%	$85.4008	$85.40	$85.40	$85.40
7 purchase totals =	$666.84		$712.1957	$712.19	$712.15	$712.20