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	$53.37	3.629%	$55.3068	$55.31	$55.30	$55.30
Purchase #2	$146.79	6.805%	$156.7791	$156.78	$156.80	$156.80
Purchase #3	$137.41	10.591%	$151.9631	$151.96	$151.95	$152.00
Purchase #4	$31.85	6.183%	$33.8193	$33.82	$33.80	$33.80
Purchase #5	$101.49	5.656%	$107.2303	$107.23	$107.25	$107.20
Purchase #6	$233.63	11.654%	$260.8572	$260.86	$260.85	$260.90
Purchase #7	$93.82	10.194%	$103.384	$103.38	$103.40	$103.40
7 purchase totals =	$798.36		$869.3398	$869.34	$869.35	$869.40