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	$202.63	4.429%	$211.6045	$211.60	$211.60	$211.60
Purchase #2	$249.30	9.668%	$273.4023	$273.40	$273.40	$273.40
Purchase #3	$28.99	8.165%	$31.357	$31.36	$31.35	$31.40
Purchase #4	$40.33	8.823%	$43.8883	$43.89	$43.90	$43.90
Purchase #5	$73.33	7.146%	$78.5702	$78.57	$78.55	$78.60
Purchase #6	$41.59	9.137%	$45.3901	$45.39	$45.40	$45.40
Purchase #7	$147.67	4.767%	$154.7094	$154.71	$154.70	$154.70
7 purchase totals =	$783.84		$838.9218	$838.92	$838.90	$839.00