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	$89.98	12.521%	$101.2464	$101.25	$101.25	$101.20
Purchase #2	$82.78	13.807%	$94.2094	$94.21	$94.20	$94.20
Purchase #3	$145.89	3.745%	$151.3536	$151.35	$151.35	$151.40
Purchase #4	$111.41	10.869%	$123.5192	$123.52	$123.50	$123.50
Purchase #5	$25.29	12.648%	$28.4887	$28.49	$28.50	$28.50
Purchase #6	$147.44	7.743%	$158.8563	$158.86	$158.85	$158.90
Purchase #7	$73.80	11.389%	$82.2051	$82.21	$82.20	$82.20
7 purchase totals =	$676.59		$739.8787	$739.89	$739.85	$739.90