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	$240.78	3.683%	$249.6479	$249.65	$249.65	$249.60
Purchase #2	$41.36	10.229%	$45.5907	$45.59	$45.60	$45.60
Purchase #3	$142.89	12.405%	$160.6155	$160.62	$160.60	$160.60
Purchase #4	$172.79	7.625%	$185.9652	$185.97	$185.95	$186.00
Purchase #5	$242.44	12.776%	$273.4141	$273.41	$273.40	$273.40
Purchase #6	$98.76	12.791%	$111.3924	$111.39	$111.40	$111.40
Purchase #7	$93.69	4.691%	$98.085	$98.09	$98.10	$98.10
7 purchase totals =	$1,032.71		$1,124.7108	$1,124.72	$1,124.70	$1,124.70