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	$248.44	10.439%	$274.3747	$274.37	$274.35	$274.40
Purchase #2	$183.82	7.864%	$198.2756	$198.28	$198.30	$198.30
Purchase #3	$139.58	12.402%	$156.8907	$156.89	$156.90	$156.90
Purchase #4	$168.98	13.118%	$191.1468	$191.15	$191.15	$191.10
Purchase #5	$57.57	9.314%	$62.9321	$62.93	$62.95	$62.90
Purchase #6	$124.72	8.623%	$135.4746	$135.47	$135.45	$135.50
Purchase #7	$93.56	5.155%	$98.383	$98.38	$98.40	$98.40
7 purchase totals =	$1,016.67		$1,117.4775	$1,117.47	$1,117.50	$1,117.50