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	$226.89	6.840%	$242.4093	$242.41	$242.40	$242.40
Purchase #2	$201.89	9.774%	$221.6227	$221.62	$221.60	$221.60
Purchase #3	$65.86	11.753%	$73.6005	$73.60	$73.60	$73.60
Purchase #4	$245.79	7.796%	$264.9518	$264.95	$264.95	$265.00
Purchase #5	$123.52	3.315%	$127.6147	$127.61	$127.60	$127.60
Purchase #6	$222.36	6.361%	$236.5043	$236.50	$236.50	$236.50
Purchase #7	$164.34	9.394%	$179.7781	$179.78	$179.80	$179.80
7 purchase totals =	$1,250.65		$1,346.4814	$1,346.47	$1,346.45	$1,346.50