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	$95.94	3.316%	$99.1214	$99.12	$99.10	$99.10
Purchase #2	$71.25	10.770%	$78.9236	$78.92	$78.90	$78.90
Purchase #3	$131.74	3.615%	$136.5024	$136.50	$136.50	$136.50
Purchase #4	$159.84	13.849%	$181.9762	$181.98	$182.00	$182.00
Purchase #5	$162.84	13.689%	$185.1312	$185.13	$185.15	$185.10
Purchase #6	$119.62	13.316%	$135.5486	$135.55	$135.55	$135.50
Purchase #7	$40.56	4.576%	$42.416	$42.42	$42.40	$42.40
7 purchase totals =	$781.79		$859.6194	$859.62	$859.60	$859.50