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	$90.80	12.758%	$102.3843	$102.38	$102.40	$102.40
Purchase #2	$179.88	9.249%	$196.5171	$196.52	$196.50	$196.50
Purchase #3	$137.57	9.566%	$150.7299	$150.73	$150.75	$150.70
Purchase #4	$247.27	13.560%	$280.7998	$280.80	$280.80	$280.80
Purchase #5	$9.86	11.813%	$11.0248	$11.02	$11.00	$11.00
Purchase #6	$199.70	9.597%	$218.8652	$218.87	$218.85	$218.90
Purchase #7	$85.88	6.421%	$91.3944	$91.39	$91.40	$91.40
7 purchase totals =	$950.96		$1,051.7155	$1,051.71	$1,051.70	$1,051.70