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	$172.44	3.811%	$179.0117	$179.01	$179.00	$179.00
Purchase #2	$29.37	11.648%	$32.791	$32.79	$32.80	$32.80
Purchase #3	$82.29	10.331%	$90.7914	$90.79	$90.80	$90.80
Purchase #4	$198.51	4.197%	$206.8415	$206.84	$206.85	$206.80
Purchase #5	$209.74	11.649%	$234.1726	$234.17	$234.15	$234.20
Purchase #6	$150.59	9.544%	$164.9623	$164.96	$164.95	$165.00
Purchase #7	$32.89	13.113%	$37.2029	$37.20	$37.20	$37.20
7 purchase totals =	$875.83		$945.7734	$945.76	$945.75	$945.80