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	$188.67	4.108%	$196.4206	$196.42	$196.40	$196.40
Purchase #2	$55.76	8.210%	$60.3379	$60.34	$60.35	$60.30
Purchase #3	$152.54	12.219%	$171.1789	$171.18	$171.20	$171.20
Purchase #4	$6.87	8.316%	$7.4413	$7.44	$7.45	$7.40
Purchase #5	$66.54	8.258%	$72.0349	$72.03	$72.05	$72.00
Purchase #6	$6.67	5.573%	$7.0417	$7.04	$7.05	$7.00
Purchase #7	$60.29	5.170%	$63.407	$63.41	$63.40	$63.40
7 purchase totals =	$537.34		$577.8623	$577.86	$577.90	$577.70