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	$179.40	8.328%	$194.3404	$194.34	$194.35	$194.30
Purchase #2	$245.74	12.120%	$275.5237	$275.52	$275.50	$275.50
Purchase #3	$149.71	10.127%	$164.8711	$164.87	$164.85	$164.90
Purchase #4	$44.32	7.146%	$47.4871	$47.49	$47.50	$47.50
Purchase #5	$244.25	12.173%	$273.9826	$273.98	$274.00	$274.00
Purchase #6	$90.63	6.490%	$96.5119	$96.51	$96.50	$96.50
Purchase #7	$154.60	6.154%	$164.1141	$164.11	$164.10	$164.10
7 purchase totals =	$1,108.65		$1,216.8309	$1,216.82	$1,216.80	$1,216.80