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	$131.33	8.574%	$142.5902	$142.59	$142.60	$142.60
Purchase #2	$182.38	9.217%	$199.19	$199.19	$199.20	$199.20
Purchase #3	$186.39	6.705%	$198.8874	$198.89	$198.90	$198.90
Purchase #4	$90.88	6.608%	$96.8854	$96.89	$96.90	$96.90
Purchase #5	$218.38	4.597%	$228.4189	$228.42	$228.40	$228.40
Purchase #6	$53.46	10.730%	$59.1963	$59.20	$59.20	$59.20
Purchase #7	$238.47	9.442%	$260.9863	$260.99	$261.00	$261.00
7 purchase totals =	$1,101.29		$1,186.1545	$1,186.17	$1,186.20	$1,186.20