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	$18.40	11.577%	$20.5302	$20.53	$20.55	$20.50
Purchase #2	$227.46	9.575%	$249.2393	$249.24	$249.25	$249.20
Purchase #3	$198.48	5.561%	$209.5175	$209.52	$209.50	$209.50
Purchase #4	$95.82	6.122%	$101.6861	$101.69	$101.70	$101.70
Purchase #5	$59.46	13.171%	$67.2915	$67.29	$67.30	$67.30
Purchase #6	$101.83	5.586%	$107.5182	$107.52	$107.50	$107.50
Purchase #7	$76.98	3.540%	$79.7051	$79.71	$79.70	$79.70
7 purchase totals =	$778.43		$835.4879	$835.50	$835.50	$835.40