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	$168.27	12.574%	$189.4283	$189.43	$189.45	$189.40
Purchase #2	$34.46	12.630%	$38.8123	$38.81	$38.80	$38.80
Purchase #3	$241.42	13.794%	$274.7215	$274.72	$274.70	$274.70
Purchase #4	$247.49	6.470%	$263.5026	$263.50	$263.50	$263.50
Purchase #5	$37.87	10.851%	$41.9793	$41.98	$42.00	$42.00
Purchase #6	$236.45	13.122%	$267.477	$267.48	$267.50	$267.50
Purchase #7	$19.89	5.365%	$20.9571	$20.96	$20.95	$21.00
7 purchase totals =	$985.85		$1,096.8781	$1,096.88	$1,096.90	$1,096.90