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	$46.97	12.319%	$52.7562	$52.76	$52.75	$52.80
Purchase #2	$49.96	11.589%	$55.7499	$55.75	$55.75	$55.70
Purchase #3	$178.91	13.787%	$203.5763	$203.58	$203.60	$203.60
Purchase #4	$160.71	12.109%	$180.1704	$180.17	$180.15	$180.20
Purchase #5	$73.50	12.683%	$82.822	$82.82	$82.80	$82.80
Purchase #6	$43.36	4.345%	$45.244	$45.24	$45.25	$45.20
Purchase #7	$246.35	3.465%	$254.886	$254.89	$254.90	$254.90
7 purchase totals =	$799.76		$875.2048	$875.21	$875.20	$875.20