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	$106.63	12.404%	$119.8564	$119.86	$119.85	$119.90
Purchase #2	$80.43	9.541%	$88.1038	$88.10	$88.10	$88.10
Purchase #3	$79.41	9.844%	$87.2271	$87.23	$87.25	$87.20
Purchase #4	$168.31	12.190%	$188.827	$188.83	$188.85	$188.80
Purchase #5	$143.40	9.367%	$156.8323	$156.83	$156.85	$156.80
Purchase #6	$65.89	11.312%	$73.3435	$73.34	$73.35	$73.30
Purchase #7	$67.77	9.745%	$74.3742	$74.37	$74.35	$74.40
7 purchase totals =	$711.84		$788.5643	$788.56	$788.60	$788.50