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	$183.71	11.119%	$204.1367	$204.14	$204.15	$204.10
Purchase #2	$209.41	13.705%	$238.1096	$238.11	$238.10	$238.10
Purchase #3	$232.33	3.410%	$240.2525	$240.25	$240.25	$240.30
Purchase #4	$98.94	8.446%	$107.2965	$107.30	$107.30	$107.30
Purchase #5	$83.74	7.661%	$90.1553	$90.16	$90.15	$90.20
Purchase #6	$60.59	11.279%	$67.4239	$67.42	$67.40	$67.40
Purchase #7	$39.28	8.437%	$42.5941	$42.59	$42.60	$42.60
7 purchase totals =	$908.00		$989.9686	$989.97	$989.95	$990.00