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	$115.63	13.496%	$131.2354	$131.24	$131.25	$131.20
Purchase #2	$64.73	13.227%	$73.2918	$73.29	$73.30	$73.30
Purchase #3	$179.51	5.632%	$189.62	$189.62	$189.60	$189.60
Purchase #4	$154.51	6.654%	$164.7911	$164.79	$164.80	$164.80
Purchase #5	$51.45	7.377%	$55.2455	$55.25	$55.25	$55.20
Purchase #6	$65.34	11.555%	$72.89	$72.89	$72.90	$72.90
Purchase #7	$101.28	12.769%	$114.2124	$114.21	$114.20	$114.20
7 purchase totals =	$732.45		$801.2862	$801.29	$801.30	$801.20