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	$64.86	12.833%	$73.1835	$73.18	$73.20	$73.20
Purchase #2	$176.40	12.767%	$198.921	$198.92	$198.90	$198.90
Purchase #3	$94.45	7.407%	$101.4459	$101.45	$101.45	$101.40
Purchase #4	$53.58	11.158%	$59.5585	$59.56	$59.55	$59.60
Purchase #5	$78.28	5.259%	$82.3967	$82.40	$82.40	$82.40
Purchase #6	$206.82	10.799%	$229.1545	$229.15	$229.15	$229.20
Purchase #7	$89.61	10.681%	$99.1812	$99.18	$99.20	$99.20
7 purchase totals =	$764.00		$843.8413	$843.84	$843.85	$843.90