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	$80.59	12.768%	$90.8797	$90.88	$90.90	$90.90
Purchase #2	$143.96	4.300%	$150.1503	$150.15	$150.15	$150.20
Purchase #3	$200.73	8.473%	$217.7379	$217.74	$217.75	$217.70
Purchase #4	$202.84	6.556%	$216.1382	$216.14	$216.15	$216.10
Purchase #5	$25.74	7.623%	$27.7022	$27.70	$27.70	$27.70
Purchase #6	$63.53	13.539%	$72.1313	$72.13	$72.15	$72.10
Purchase #7	$103.85	11.430%	$115.7201	$115.72	$115.70	$115.70
7 purchase totals =	$821.24		$890.4597	$890.46	$890.50	$890.40