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	$71.99	11.793%	$80.4798	$80.48	$80.50	$80.50
Purchase #2	$96.41	7.783%	$103.9136	$103.91	$103.90	$103.90
Purchase #3	$139.96	7.336%	$150.2275	$150.23	$150.25	$150.20
Purchase #4	$240.98	13.800%	$274.2352	$274.24	$274.25	$274.20
Purchase #5	$57.59	12.603%	$64.8481	$64.85	$64.85	$64.80
Purchase #6	$233.47	12.629%	$262.9549	$262.95	$262.95	$263.00
Purchase #7	$151.82	13.203%	$171.8648	$171.86	$171.85	$171.90
7 purchase totals =	$992.22		$1,108.5239	$1,108.52	$1,108.55	$1,108.50