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	$96.36	9.106%	$105.1345	$105.13	$105.15	$105.10
Purchase #2	$157.69	7.177%	$169.0074	$169.01	$169.00	$169.00
Purchase #3	$29.61	13.369%	$33.5686	$33.57	$33.55	$33.60
Purchase #4	$82.92	7.790%	$89.3795	$89.38	$89.40	$89.40
Purchase #5	$98.83	10.442%	$109.1498	$109.15	$109.15	$109.10
Purchase #6	$247.59	11.838%	$276.8997	$276.90	$276.90	$276.90
Purchase #7	$83.98	3.479%	$86.9017	$86.90	$86.90	$86.90
7 purchase totals =	$796.98		$870.0412	$870.04	$870.05	$870.00