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	$39.90	3.691%	$41.3727	$41.37	$41.35	$41.40
Purchase #2	$31.37	6.104%	$33.2848	$33.28	$33.30	$33.30
Purchase #3	$149.31	10.194%	$164.5307	$164.53	$164.55	$164.50
Purchase #4	$48.32	3.774%	$50.1436	$50.14	$50.15	$50.10
Purchase #5	$44.62	6.254%	$47.4105	$47.41	$47.40	$47.40
Purchase #6	$202.25	9.780%	$222.0301	$222.03	$222.05	$222.00
Purchase #7	$38.53	7.666%	$41.4837	$41.48	$41.50	$41.50
7 purchase totals =	$554.30		$600.2561	$600.24	$600.30	$600.20