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	$152.77	9.706%	$167.5979	$167.60	$167.60	$167.60
Purchase #2	$212.92	13.692%	$242.073	$242.07	$242.05	$242.10
Purchase #3	$65.71	8.301%	$71.1646	$71.16	$71.15	$71.20
Purchase #4	$6.41	11.544%	$7.15	$7.15	$7.15	$7.20
Purchase #5	$150.98	13.392%	$171.1992	$171.20	$171.20	$171.20
Purchase #6	$39.31	8.856%	$42.7913	$42.79	$42.80	$42.80
Purchase #7	$75.90	8.815%	$82.5906	$82.59	$82.60	$82.60
7 purchase totals =	$704.00		$784.5666	$784.56	$784.55	$784.70