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	$250.80	10.216%	$276.4217	$276.42	$276.40	$276.40
Purchase #2	$81.60	11.821%	$91.2459	$91.25	$91.25	$91.20
Purchase #3	$221.44	13.745%	$251.8769	$251.88	$251.90	$251.90
Purchase #4	$246.57	7.305%	$264.5819	$264.58	$264.60	$264.60
Purchase #5	$213.61	4.814%	$223.8932	$223.89	$223.90	$223.90
Purchase #6	$90.89	12.406%	$102.1658	$102.17	$102.15	$102.20
Purchase #7	$171.94	6.251%	$182.688	$182.69	$182.70	$182.70
7 purchase totals =	$1,276.85		$1,392.8734	$1,392.88	$1,392.90	$1,392.90