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	$21.99	3.726%	$22.8093	$22.81	$22.80	$22.80
Purchase #2	$152.94	10.421%	$168.8779	$168.88	$168.90	$168.90
Purchase #3	$228.44	7.590%	$245.7786	$245.78	$245.80	$245.80
Purchase #4	$120.48	12.674%	$135.7496	$135.75	$135.75	$135.70
Purchase #5	$102.39	8.470%	$111.0624	$111.06	$111.05	$111.10
Purchase #6	$82.91	7.458%	$89.0934	$89.09	$89.10	$89.10
Purchase #7	$13.40	11.228%	$14.9046	$14.90	$14.90	$14.90
7 purchase totals =	$722.55		$788.2758	$788.27	$788.30	$788.30