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	$93.54	7.254%	$100.3254	$100.33	$100.35	$100.30
Purchase #2	$31.45	3.421%	$32.5259	$32.53	$32.55	$32.50
Purchase #3	$69.73	3.562%	$72.2138	$72.21	$72.20	$72.20
Purchase #4	$184.88	12.604%	$208.1823	$208.18	$208.20	$208.20
Purchase #5	$201.60	11.518%	$224.8203	$224.82	$224.80	$224.80
Purchase #6	$133.40	5.806%	$141.1452	$141.15	$141.15	$141.10
Purchase #7	$12.40	3.246%	$12.8025	$12.80	$12.80	$12.80
7 purchase totals =	$727.00		$792.0154	$792.02	$792.05	$791.90