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	$69.62	9.705%	$76.3766	$76.38	$76.40	$76.40
Purchase #2	$135.54	3.166%	$139.8312	$139.83	$139.85	$139.80
Purchase #3	$142.27	6.527%	$151.556	$151.56	$151.55	$151.60
Purchase #4	$79.80	7.171%	$85.5225	$85.52	$85.50	$85.50
Purchase #5	$72.46	11.872%	$81.0625	$81.06	$81.05	$81.10
Purchase #6	$196.33	6.672%	$209.4291	$209.43	$209.45	$209.40
Purchase #7	$140.83	13.747%	$160.1899	$160.19	$160.20	$160.20
7 purchase totals =	$836.85		$903.9678	$903.97	$904.00	$904.00