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	$123.30	3.207%	$127.2542	$127.25	$127.25	$127.30
Purchase #2	$247.63	10.380%	$273.334	$273.33	$273.35	$273.30
Purchase #3	$197.36	7.666%	$212.4896	$212.49	$212.50	$212.50
Purchase #4	$32.76	13.816%	$37.2861	$37.29	$37.30	$37.30
Purchase #5	$51.96	11.229%	$57.7946	$57.79	$57.80	$57.80
Purchase #6	$161.65	3.269%	$166.9343	$166.93	$166.95	$166.90
Purchase #7	$25.94	6.518%	$27.6308	$27.63	$27.65	$27.60
7 purchase totals =	$840.60		$902.7236	$902.71	$902.80	$902.70