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	$64.83	13.516%	$73.5924	$73.59	$73.60	$73.60
Purchase #2	$218.88	4.366%	$228.4363	$228.44	$228.45	$228.40
Purchase #3	$85.33	8.642%	$92.7042	$92.70	$92.70	$92.70
Purchase #4	$65.86	10.742%	$72.9347	$72.93	$72.95	$72.90
Purchase #5	$217.50	12.799%	$245.3378	$245.34	$245.35	$245.30
Purchase #6	$62.74	3.417%	$64.8838	$64.88	$64.90	$64.90
Purchase #7	$152.35	6.755%	$162.6412	$162.64	$162.65	$162.60
7 purchase totals =	$867.49		$940.5304	$940.52	$940.60	$940.40