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	$210.84	5.619%	$222.6871	$222.69	$222.70	$222.70
Purchase #2	$243.81	13.418%	$276.5244	$276.52	$276.50	$276.50
Purchase #3	$187.28	11.241%	$208.3321	$208.33	$208.35	$208.30
Purchase #4	$85.51	9.740%	$93.8387	$93.84	$93.85	$93.80
Purchase #5	$250.91	6.256%	$266.6069	$266.61	$266.60	$266.60
Purchase #6	$53.88	10.443%	$59.5067	$59.51	$59.50	$59.50
Purchase #7	$6.98	4.874%	$7.3202	$7.32	$7.30	$7.30
7 purchase totals =	$1,039.21		$1,134.8161	$1,134.82	$1,134.80	$1,134.70