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	$37.89	6.803%	$40.4677	$40.47	$40.45	$40.50
Purchase #2	$85.65	4.730%	$89.7012	$89.70	$89.70	$89.70
Purchase #3	$147.66	13.293%	$167.2884	$167.29	$167.30	$167.30
Purchase #4	$15.33	3.686%	$15.8951	$15.90	$15.90	$15.90
Purchase #5	$50.66	10.258%	$55.8567	$55.86	$55.85	$55.90
Purchase #6	$181.37	13.838%	$206.468	$206.47	$206.45	$206.50
Purchase #7	$131.58	13.716%	$149.6275	$149.63	$149.65	$149.60
7 purchase totals =	$650.14		$725.3046	$725.32	$725.30	$725.40