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	$128.45	11.220%	$142.8621	$142.86	$142.85	$142.90
Purchase #2	$240.89	11.834%	$269.3969	$269.40	$269.40	$269.40
Purchase #3	$106.25	4.378%	$110.9016	$110.90	$110.90	$110.90
Purchase #4	$159.80	13.551%	$181.4545	$181.45	$181.45	$181.50
Purchase #5	$77.54	5.819%	$82.0521	$82.05	$82.05	$82.10
Purchase #6	$178.83	7.223%	$191.7469	$191.75	$191.75	$191.70
Purchase #7	$240.32	5.438%	$253.3886	$253.39	$253.40	$253.40
7 purchase totals =	$1,132.08		$1,231.8027	$1,231.80	$1,231.80	$1,231.90