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	$64.27	4.725%	$67.3068	$67.31	$67.30	$67.30
Purchase #2	$168.33	10.818%	$186.5399	$186.54	$186.55	$186.50
Purchase #3	$177.71	6.820%	$189.8298	$189.83	$189.85	$189.80
Purchase #4	$90.54	9.837%	$99.4464	$99.45	$99.45	$99.40
Purchase #5	$76.92	6.442%	$81.8752	$81.88	$81.90	$81.90
Purchase #6	$27.25	7.206%	$29.2136	$29.21	$29.20	$29.20
Purchase #7	$160.74	7.421%	$172.6685	$172.67	$172.65	$172.70
7 purchase totals =	$765.76		$826.8802	$826.89	$826.90	$826.80